1078 lines
36 KiB
ArmAsm
1078 lines
36 KiB
ArmAsm
;-----------------------------------------------------;
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; VTL-2 for the 6502 (VTL02C) ;
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; Original Altair 680b version by ;
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; Frank McCoy and Gary Shannon 1977 ;
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; 2012: Adapted to the 6502 by Michael T. Barry ;
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; Thanks to sbprojects.com for a very nice assembler! ;
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;-----------------------------------------------------;
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; Copyright (c) 2012, Michael T. Barry
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; Revision B (c) 2015, Michael T. Barry
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; Revision C (c) 2015, Michael T. Barry
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; All rights reserved.
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;
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; 2019-07-31 (marcelk) Adapted for as65 assembler
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; and Gigatron TTL computer
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;
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; Redistribution and use in source and binary forms,
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; with or without modification, are permitted,
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; provided that the following conditions are met:
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;
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; 1. Redistributions of source code must retain the
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; above copyright notice, this list of conditions
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; and the following disclaimer.
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; 2. Redistributions in binary form must reproduce the
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; above copyright notice, this list of conditions
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; and the following disclaimer in the documentation
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; and/or other materials provided with the
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; distribution.
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;
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; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS
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; AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED
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; WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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; IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
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; SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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; FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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; EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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; SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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; INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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; LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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; OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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; IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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; ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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;-----------------------------------------------------;
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; Except for the differences discussed below, VTL02 was
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; designed to duplicate the OFFICIALLY DOCUMENTED
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; behavior of Frank's 680b version, detailed here:
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; http://www.altair680kit.com/manuals/Altair_
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; 680-VTL-2%20Manual-05-Beta_1-Searchable.pdf
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; These versions ignore all syntax errors and plow
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; through VTL-2 programs with the assumption that
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; they are "correct", but in their own unique ways,
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; so any claims of compatibility are null and void
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; for VTL-2 code brave (or stupid) enough to stray
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; from the beaten path.
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;
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; Differences between the 680b and 6502 versions:
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; * {&} and {*} are initialized on entry.
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; * Division by zero returns 65535 for the quotient and
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; the dividend for the remainder (the original 6800
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; version froze).
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; * The 6502 has NO 16-bit registers (other than PC)
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; and less overall register space than the 6800,
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; so the interpreter reserves some obscure VTL02C
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; variables {@ $ ( ) 0 1 2 3 4 5 6 7 8 9 < > : ?}
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; for its internal use (the 680b version used a
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; similar tactic, but differed in the details).
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; The deep nesting of parentheses also puts {; < =}
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; in danger of corruption. For example, executing
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; the statement A=((((((((1)))))))) sets both {A}
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; and {;} to the value 1.
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; * Users wishing to call a machine language subroutine
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; via the system variable {>} must first set the
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; system variable {"} to the proper address vector
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; (for example, "=768).
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; * The x register is used to point to a simple VTL02C
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; variable (it can't point explicitly to an array
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; element like the 680b version because it's only
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; 8-bits). In the comments, var[x] refers to the
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; 16-bit contents of the zero-page variable pointed
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; to by register x (residing at addresses x, x+1).
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; * The y register is used as a pointer offset inside
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; a VTL02C statement (easily handling the maximum
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; statement length of about 128 bytes). In the
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; comments, @[y] refers to the 16-bit address
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; formed by adding register y to the value in {@}.
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; * The structure and flow of this interpreter are
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; similar to the 680b version, but have been
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; reorganized in a more 6502-friendly format (the
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; 6502 has no 'bsr' instruction, so the 'stuffing'
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; of subroutines within 128 bytes of the caller is
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; only advantageous for conditional branches).
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; * This version is based on the original port, which
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; was wound rather tightly, in a failed attempt to
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; fit it into 768 bytes like the 680b version; many
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; structured programming principles were sacrificed
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; in that effort. The 6502 simply requires more
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; instructions than the 6800 does to manipulate 16-
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; bit quantities, but the overall execution speed
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; should be comparable due to the 6502's slightly
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; lower average clocks/instruction ratio. As it is
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; now, it fits into 1KB with just a few bytes to
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; spare, but is more feature-laden than the 680b
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; interpreter whence it came. Beginning with
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; Revision C, I tried to strike a tasteful balance
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; between execution speed and code size, but I
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; stubbornly kept it under 1024 ROMable bytes and
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; used only documented op-codes that were supported
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; by the original NMOS 6502 (without the ROR bug).
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; I may have missed a few optimizations -- further
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; suggestions are welcome.
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; * VTL02C is my free gift (?) to the world. It may be
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; freely copied, shared, and/or modified by anyone
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; interested in doing so, with only the stipulation
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; that any liabilities arising from its use are
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; limited to the price of VTL02C (nothing).
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;-----------------------------------------------------;
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; 2015: Revision B included some space optimizations
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; (suggested by dclxvi) and enhancements
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; (suggested by mkl0815 and Klaus2m5):
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;
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; * Bit-wise operators & | ^ (and, or, xor)
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; Example: A=$|128) Get a char and set hi-bit
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;
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; * Absolute addressed 8-bit memory load and store
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; via the {< @} facility:
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; Example: <=P) Point to the I/O port at P
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; @=@&254^128) Clear low-bit & flip hi-bit
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;
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; * Starting with VTL02B, the space character is no
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; longer a valid user variable nor a "valid" binary
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; operator. It's now only significant as a numeric
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; constant terminator and as a place-holder in
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; strings and program listings, where it may be
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; used to improve human readability (at a slight
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; cost in execution speed and memory consumption).
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; Example:
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; * (VTL-2)
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; 1000 A=1) Init loop index
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; 1010 ?=A) Print index
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; 1020 ?="") Newline
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; 1030 A=A+1) Update index
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; 1040 #=A<10*1010) Loop until done
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;
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; * (VTL02B)
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; 1000 A = 1 ) Init loop index
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; 1010 ? = A ) Print index
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; 1020 ? = "" ) Newline
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; 1030 A = A + 1 ) Update index
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; 1040 # = A < 10 * 1010 ) Loop until done
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;
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; 2015: Revision C includes further enhancements
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; (suggested by Klaus2m5):
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;
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; * "THEN" and "ELSE" operators [ ]
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; A[B returns 0 if A is 0, otherwise returns B.
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; A]B returns B if A is 0, otherwise returns 0.
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;
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; * Some effort was made to balance interpreter code
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; density with interpreter performance, while
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; remaining within the 1KB constraint. Structured
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; programming principles remained at low priority.
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;-----------------------------------------------------;
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; VTL02C variables occupy RAM addresses $0080 to $00ff,
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; and are little-endian, in the 6502 tradition.
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; The use of lower-case and some control characters for
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; variable names is allowed, but not recommended; any
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; attempts to do so would likely result in chaos, due
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; to aliasing with upper-case and system variables.
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; Variables tagged with an asterisk are used internally
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; by the interpreter and may change without warning.
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; {@ $ ( ) 0..9 : > ?} are (usually) intercepted by
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; the interpreter, so their internal use by VTL02C is
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; "safe". The same cannot be said for {; < =}, so be
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; careful!
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at = $c0 ; {@}* internal pointer / mem byte
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; VTL02C standard user variable space
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; {A B C .. X Y Z [ \ ] ^ _}
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; VTL02C system variable space
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;space = $80 ; { } Starting with VTL02B: the
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; space character is no longer a
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; valid user variable nor a
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; "valid" binary operator.
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; It is now only significant as a
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; numeric constant terminator and
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; as a place-holder in strings
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; and program listings.
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bang = $82 ; {!} return line number
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quote = $84 ; {"} user ml subroutine vector
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pound = $86 ; {#} current line number
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dolr = $88 ; {$}* temp storage / char i/o
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remn = $8a ; {%} remainder of last division
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ampr = $8c ; {&} pointer to start of array
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tick = $8e ; {'} pseudo-random number
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lparen = $90 ; {(}* old line # / begin sub-exp
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rparen = $92 ; {)}* temp storage / end sub-exp
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star = $94 ; {*} pointer to end of free mem
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; $96 ; {+ , - . /} valid variables
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; Interpreter argument stack space
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arg = $a0 ; {0 1 2 3 4 5 6 7 8 9 :}*
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; Rarely used variables and argument stack overflow
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; $b6 ; {;}* valid user variable
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lthan = $b8 ; {<}* user memory byte pointer
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; = $ba ; {=}* valid user variable
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gthan = $bc ; {>}* temp / call ML subroutine
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ques = $be ; {?}* temp / terminal i/o
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;
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nulstk = $007f ; [Gigatron] v6502 stack in page 0
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;-----------------------------------------------------;
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; Equates for a 48K+ Apple 2 (original, +, e, c, gs)
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ESC = 27 ; "Cancel current input line" key
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BS = $5f ; "Delete last keypress" key [Gigatron]
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OP_OR = '!' ; Bit-wise OR operator
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linbuf = $0200 ; input line buffer
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prgm = $0700 ; VTL02B program grows from here
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himem = $0800 ; ... up to the top of user RAM
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vtl02c = $0219 ; interpreter cold entry point [Gigatron]
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; (warm entry point is startok)
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;KBD = $c000 ; 128 + keypress if waiting
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serialRaw = $0f
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;KEYIN = $fd0c ; apple monitor keyin routine
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;COUT = $fded ; apple monitor charout routine
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;=====================================================;
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.org $200
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.byte 0,0,0,0,0,0,0,0
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.byte 0,0,0,0,0,0,0,0
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.byte 0,0,0,0,0,0,0,0
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.byte 0
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; [Gigatron] line buffer can go 16 bytes into
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; vtl02c for 41 bytes total
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.org vtl02c
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;-----------------------------------------------------;
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; Initialize program area pointers and start VTL02C
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; 17 bytes
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lda #<prgm
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sta ampr ; {&} -> empty program
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lda #>prgm
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sta ampr+1
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lda #<himem
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sta star ; {*} -> top of user RAM
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lda #>himem
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sta star+1
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startok:
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sec ; request "OK" message
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; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
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; Start/restart VTL02C command line with program intact
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; 32 bytes
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start:
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cld ; a sensible precaution
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ldx #<nulstk
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txs ; drop whatever is on the stack
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bcc user ; skip "OK" if carry clear
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jsr outnl
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lda #'O' ; output \nOK\n to terminal
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jsr outch
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lda #'K'
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jsr outch
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jsr outnl
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user:
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jsr inln ; input a line from the user
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ldx #pound ; cvbin destination = {#}
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jsr cvbin ; does line start with a number?
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beq direct ; no: execute direct statement
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; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
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; Delete/insert/replace program line or list program
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; 7 bytes
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stmnt:
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clc
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lda pound
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ora pound+1 ; {#} = 0?
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bne skp2 ; no: delete/insert/replace line
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; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
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; List program to terminal and restart "OK" prompt
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; entry: Carry must be clear
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; uses: findln:, outch:, prnum:, prstr:, {@ ( )}
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; exit: to command line via findln:
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; 20 bytes
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list_:
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jsr findln ; find program line >= {#}
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ldx #lparen ; line number for prnum
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jsr prnum ; print the line number
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lda #' ' ; print a space instead of the
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jsr outch ; line length byte
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lda #0 ; zero for delimiter
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jsr prstr ; print the rest of the line
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bcs list_ ; (always taken)
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;-----------------------------------------------------;
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; The main program execution loop
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; entry: with (cs) via "beq direct" in user:
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; exit: to command line via findln: or "beq start"
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; 45 bytes
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progr:
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beq eloop0 ; if {#} = 0 then ignore and
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ldy lparen+1 ; continue (false branch)
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ldx lparen ; else did {#} change?
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cpy pound+1 ; yes: perform a branch, with
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bne branch ; carry flag conditioned for
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cpx pound ; the appropriate direction.
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beq eloop ; no: execute next line (cs)
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branch:
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inx ; execute a VTL02B branch
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bne branch2
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iny
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branch2:
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stx bang ; {!} = {(} + 1 (return ptr)
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sty bang+1
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eloop0:
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rol
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eor #1 ; complement carry flag
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ror
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eloop:
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jsr findln ; find first/next line >= {#}
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iny ; skip over the length byte
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direct:
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php ; (cc: program, cs: direct)
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jsr exec ; execute one VTL02B statement
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plp
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lda pound ; update Z for {#}
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ora pound+1 ; if program mode then continue
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bcc progr ; if direct mode, did {#} change?
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beq start ; no: restart "OK" prompt
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bne eloop0 ; yes: execute program from {#}
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;-----------------------------------------------------;
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; Delete/insert/replace program line and restart the
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; command prompt (no "OK" means success)
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; entry: Carry must be clear
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; uses: find:, start:, linbuf, {@ > # & * (}
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; 151 bytes
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skp2:
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tya ; save linbuf offset pointer
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pha
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jsr find ; point {@} to first line >= {#}
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bcs insrt
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eor pound ; if line doesn't already exist
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bne insrt ; then skip deletion process
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cpx pound+1
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bne insrt
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tax ; x = 0
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lda (at),y
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tay ; y = length of line to delete
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eor #255
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adc ampr ; {&} = {&} - y
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sta ampr
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bcs delt
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dec ampr+1
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delt:
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lda at
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sta gthan ; {>} = {@}
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lda at+1
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sta gthan+1
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delt2:
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lda gthan
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cmp ampr ; delete the line
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lda gthan+1
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sbc ampr+1
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bcs insrt
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lda (gthan),y
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sta (gthan,x)
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inc gthan
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bne delt2
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inc gthan+1
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bcc delt2 ; (always taken)
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insrt:
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pla
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tax ; x = linbuf offset pointer
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lda pound
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pha ; push the new line number on
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lda pound+1 ; the system stack
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pha
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ldy #2
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cntln:
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inx
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iny ; determine new line length in y
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lda linbuf-1,x ; and push statement string on
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pha ; the system stack
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bne cntln
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cpy #4 ; if empty line then skip the
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bcc jstart ; insertion process
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tax ; x = 0
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tya
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clc
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adc ampr ; calculate new program end
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sta gthan ; {>} = {&} + y
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txa
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adc ampr+1
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sta gthan+1
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lda gthan
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cmp star ; if {>} >= {*} then the program
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lda gthan+1 ; won't fit in available RAM,
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sbc star+1 ; so drop the stack and abort
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bcs jstart ; to the "OK" prompt
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slide:
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lda ampr
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bne slide2
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dec ampr+1
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slide2:
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dec ampr
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lda ampr
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cmp at
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lda ampr+1
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sbc at+1
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bcc move ; slide open a gap inside the
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lda (ampr,x) ; program just big enough to
|
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sta (ampr),y ; hold the new line
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bcs slide ; (always taken)
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move:
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tya
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tax ; x = new line length
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move2:
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pla ; pull the statement string and
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dey ; the new line number and store
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sta (at),y ; them in the program gap
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bne move2
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ldy #2
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txa
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sta (at),y ; store length after line number
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lda gthan
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sta ampr ; {&} = {>}
|
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lda gthan+1
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sta ampr+1
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jstart:
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jmp start ; drop stack, restart cmd prompt
|
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;-----------------------------------------------------;
|
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; Point @[y] to the first/next program line >= {#}
|
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; entry: (cc): start search at beginning of program
|
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; (cs): start search at next line
|
|
; ({@} -> beginning of current line)
|
|
; used by: list_:, progr:
|
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; uses: find:, jstart:, prgm, {@ # & (}
|
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; exit: if line not found then abort to "OK" prompt
|
|
; else {@} -> found line, x:a = {#} = {(} =
|
|
; actual line number, y = 2, (cc)
|
|
; 10 bytes
|
|
findln:
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jsr find ; find first/next line >= {#}
|
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bcs jstart ; if end then restart "OK" prompt
|
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sta pound ; {#} = {(}
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stx pound+1
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rts
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;-----------------------------------------------------;
|
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; {?="...} handler; called from exec:
|
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; List line handler; called from list_:
|
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; 2 bytes
|
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prstr:
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iny ; skip over the " or length byte
|
|
tax ; x = delimiter, fall through
|
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; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
|
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; Print a string at @[y]
|
|
; x holds the delimiter char, which is skipped over,
|
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; not printed (a null byte is always a delimiter)
|
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; If a key was pressed, it pauses for another keypress
|
|
; before returning. If either of those keys was a
|
|
; ctrl-C, it drops the stack and restarts the "OK"
|
|
; prompt with the user program intact
|
|
; entry: @[y] -> string, x = delimiter char
|
|
; uses: inch:, inkey:, jstart:, outch:, execrts:
|
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; exit: (normal) @[y] -> null or byte after delimiter
|
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; (ctrl-C) drop the stack & restart "OK" prompt
|
|
; 39 bytes
|
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prmsg:
|
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txa
|
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cmp (at),y ; found delimiter or null?
|
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beq prmsg2 ; yes: finish up
|
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lda (at),y
|
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beq prmsg2
|
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jsr outch ; no: print char to terminal
|
|
iny ; and loop (with safety escape)
|
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bpl prmsg
|
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prmsg2:
|
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tax ; save closing delimiter
|
|
jsr inkey ; any key = pause?
|
|
; [Gigatron] inkey handles the second key already
|
|
;beq prout ; no: proceed
|
|
;jsr inch ; yes: wait for another key
|
|
prout:
|
|
txa ; retrieve closing delimiter
|
|
beq outnl ; always \n after null delimiter
|
|
jsr skpbyte ; skip over the delimiter
|
|
cmp #';' ; if trailing char is ';' then
|
|
beq execrts ; suppress the \n
|
|
outnl:
|
|
lda #$0d ; \n to terminal
|
|
joutch:
|
|
jmp outch
|
|
;-----------------------------------------------------;
|
|
; Execute a (hopefully) valid VTL02C statement at @[y]
|
|
; entry: @[y] -> left-side of statement
|
|
; uses: nearly everything
|
|
; exit: note to machine language subroutine {>=...}
|
|
; users: no registers or variables are
|
|
; required to be preserved except the system
|
|
; stack pointer, the text base pointer {@},
|
|
; and the original line number {(}
|
|
; if there is a {"} directly after the assignment
|
|
; operator, the statement will execute as {?="...},
|
|
; regardless of the variable named on the left side
|
|
; 84 bytes
|
|
exec:
|
|
jsr getbyte ; fetch left-side variable name
|
|
beq execrts ; do nothing with a null statement
|
|
cmp #')' ; same for a full-line comment
|
|
beq execrts
|
|
iny
|
|
ldx #arg ; initialize argument pointer
|
|
jsr convp ; arg[{0}] -> left-side variable
|
|
jsr getbyte ; skip over assignment operator
|
|
jsr skpbyte ; is right-side a literal string?
|
|
cmp #'"' ; yes: print the string with
|
|
beq prstr ; trailing ';' check & return
|
|
ldx #arg+2 ; point eval to arg[{1}]
|
|
jsr eval ; evaluate right-side in arg[{1}]
|
|
lda arg+2
|
|
ldy #0
|
|
ldx arg+1 ; was left-side an array element?
|
|
bne exec3 ; yes: skip to default actions
|
|
ldx arg
|
|
cpx #at ; if {@=...} statement then poke
|
|
beq poke ; low half of arg[{1}] to ({<})
|
|
cpx #dolr ; if {$=...} statement then print
|
|
beq joutch ; arg[{1}] as ASCII character
|
|
cpx #ques ; if {?=...} statement then print
|
|
beq prnum0 ; arg[{1}] as unsigned decimal
|
|
cpx #gthan ; if {>=...} statement then call
|
|
beq usr ; user-defined ml routine
|
|
exec3:
|
|
sta (arg),y
|
|
adc tick+1 ; store arg[{1}] in the left-side
|
|
rol ; variable
|
|
tax
|
|
iny
|
|
lda arg+3
|
|
sta (arg),y
|
|
adc tick ; pseudo-randomize {'}
|
|
rol
|
|
sta tick+1
|
|
stx tick
|
|
execrts:
|
|
rts
|
|
usr:
|
|
tax ; jump to user ml routine with
|
|
lda arg+3 ; arg[{1}] in a:x (MSB:LSB)
|
|
jmp (quote) ; {"} must point to valid 6502 code
|
|
poke:
|
|
sta (lthan),y
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; {?=...} handler; called by exec:
|
|
; 2 bytes
|
|
prnum0:
|
|
ldx #arg+2 ; x -> arg[{1}], fall through
|
|
; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
|
|
; Print an unsigned decimal number (0..65535) in var[x]
|
|
; entry: var[x] = number to print
|
|
; uses: div:, outch:, var[x+2], saves original {%}
|
|
; exit: var[x] = 0, var[x+2] = 10
|
|
; 43 bytes
|
|
prnum:
|
|
lda remn
|
|
pha ; save {%}
|
|
lda remn+1
|
|
pha
|
|
lda #0 ; null delimiter for print
|
|
pha
|
|
sta 3,x
|
|
lda #10 ; divisor = 10
|
|
sta 2,x ; repeat {
|
|
prnum2:
|
|
jsr div ; divide var[x] by 10
|
|
lda remn
|
|
ora #'0' ; convert remainder to ASCII
|
|
pha ; stack digits in ascending
|
|
lda 0,x ; order ('0' for zero)
|
|
ora 1,x
|
|
bne prnum2 ; } until var[x] is 0
|
|
pla
|
|
prnum3:
|
|
jsr outch ; print digits in descending
|
|
pla ; order until delimiter is
|
|
bne prnum3 ; encountered
|
|
pla
|
|
sta remn+1 ; restore {%}
|
|
pla
|
|
sta remn
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Evaluate a (hopefully) valid VTL02C expression at
|
|
; @[y] and place its calculated value in arg[x]
|
|
; A VTL02C expression is defined as a string of one or
|
|
; more terms, separated by operators and terminated
|
|
; with a null or an unmatched right parenthesis
|
|
; A term is defined as a variable name, a decimal
|
|
; constant, or a parenthesized sub-expression; terms
|
|
; are evaluated strictly from left to right
|
|
; A variable name is defined as a user variable, an
|
|
; array element expression enclosed in {: )}, or a
|
|
; system variable (which may have side-effects)
|
|
; entry: @[y] -> expression text, x -> argument
|
|
; uses: getval:, oper:, {@}, argument stack area
|
|
; exit: arg[x] = result, @[y] -> next text
|
|
; 31 bytes
|
|
eval:
|
|
lda #0
|
|
sta 0,x ; start evaluation by simulating
|
|
sta 1,x ; {0+expression}
|
|
lda #'+'
|
|
notdn:
|
|
pha ; stack alleged operator
|
|
inx ; advance the argument stack
|
|
inx ; pointer
|
|
jsr getval ; arg[x+2] = value of next term
|
|
dex
|
|
dex
|
|
pla ; retrieve and apply the operator
|
|
jsr oper ; to arg[x], arg[x+2]
|
|
jsr getbyte ; end of expression?
|
|
beq evalrts ; (null or right parenthesis)
|
|
iny
|
|
cmp #')' ; no: skip over the operator
|
|
bne notdn ; and continue the evaluation
|
|
evalrts:
|
|
rts ; yes: return with final result
|
|
;-----------------------------------------------------;
|
|
; Get numeric value of the term at @[y] into var[x]
|
|
; Some examples of valid terms: 123, $, H, (15-:J)/?)
|
|
; 83 bytes
|
|
getval:
|
|
jsr cvbin ; decimal number at @[y]?
|
|
bne getrts ; yes: return with it in var[x]
|
|
jsr getbyte
|
|
iny
|
|
cmp #'?' ; user line input?
|
|
bne getval2
|
|
tya ; yes:
|
|
pha
|
|
lda at ; save @[y]
|
|
pha ; (current expression ptr)
|
|
lda at+1
|
|
pha
|
|
jsr inln ; input expression from user
|
|
jsr eval ; evaluate, var[x] = result
|
|
pla
|
|
sta at+1
|
|
pla
|
|
sta at ; restore @[y]
|
|
pla
|
|
tay
|
|
rts ; skip over "?" and return
|
|
getval2:
|
|
cmp #'$' ; user char input?
|
|
bne getval2a
|
|
jsr inch ; yes: input one char
|
|
bcs getval5 ; (always taken)
|
|
getval2a:
|
|
cmp #'@' ; memory access?
|
|
bne getval3
|
|
sty dolr ; yes:
|
|
ldy #0
|
|
lda (lthan),y ; access memory byte at ({<})
|
|
ldy dolr
|
|
bne getval5 ; (always taken)
|
|
getval3:
|
|
cmp #'(' ; sub-expression?
|
|
beq eval ; yes: evaluate it recursively
|
|
jsr convp ; no: first set var[x] to the
|
|
lda (0,x) ; named variable's address,
|
|
pha ; then replace that address
|
|
inc 0,x ; with the variable's actual
|
|
bne getval4 ; value before returning
|
|
inc 1,x
|
|
getval4:
|
|
lda (0,x)
|
|
sta 1,x ; store high-byte of term value
|
|
pla
|
|
getval5:
|
|
sta 0,x ; store low-byte of term value
|
|
getrts:
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Set var[x] to the address of the variable named in a
|
|
; entry: a holds variable name, @[y] -> text holding
|
|
; array index expression (if a = ':')
|
|
; uses: plus, eval, oper8d, {@ &}
|
|
; exit: (eq): var[x] -> variable, @[y] unchanged
|
|
; (ne): var[x] -> array element,
|
|
; @[y] -> following text
|
|
; 26 bytes
|
|
convp:
|
|
cmp #':' ; array element?
|
|
bne simple ; no: var[x] -> simple variable
|
|
jsr eval ; yes: evaluate array index at
|
|
asl 0,x ; @[y] and advance y
|
|
rol 1,x
|
|
lda ampr ; var[x] -> array element
|
|
sta 2,x ; at address 2*index+&
|
|
lda ampr+1
|
|
sta 3,x
|
|
bne plus ; (always taken)
|
|
; The following section is designed to translate the
|
|
; named simple variable from its ASCII value to its
|
|
; zero-page address. In this case, 'A' translates
|
|
; to $82, '!' translates to $c2, etc. The method
|
|
; employed must correspond to the zero-page equates
|
|
; above, or strange and not-so-wonderful bugs will
|
|
; befall the weary traveller on his or her porting
|
|
; journey.
|
|
simple:
|
|
asl ; form simple variable address
|
|
;ora #$80 ; mapping function is (a*2)|128
|
|
;bmi oper8d ; (always taken)
|
|
adc #$40 ; [Gigatron] sp..'_' -> $80..$fe
|
|
bne oper8d ; [Gigatron] (always taken)
|
|
|
|
;-----------------------------------------------------;
|
|
; 16-bit unsigned multiply routine: var[x] *= var[x+2]
|
|
; exit: overflow is ignored/discarded, var[x+2] and
|
|
; {>} are modified, a = 0
|
|
; 40 bytes
|
|
mul:
|
|
lda 0,x
|
|
sta gthan
|
|
lda 1,x ; {>} = var[x]
|
|
sta gthan+1
|
|
lda #0
|
|
sta 0,x ; var[x] = 0
|
|
sta 1,x
|
|
mul2:
|
|
lda gthan
|
|
ora gthan+1
|
|
beq mulrts ; exit early if {>} = 0
|
|
lsr gthan+1
|
|
ror gthan ; {>} /= 2
|
|
bcc mul3
|
|
jsr plus ; form the product in var[x]
|
|
mul3:
|
|
asl 2,x
|
|
rol 3,x ; left-shift var[x+2]
|
|
lda 2,x
|
|
ora 3,x ; loop until var[x+2] = 0
|
|
bne mul2
|
|
mulrts:
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; var[x] += var[x+2]
|
|
; 14 bytes
|
|
plus:
|
|
clc
|
|
lda 0,x
|
|
adc 2,x
|
|
sta 0,x
|
|
lda 1,x
|
|
adc 3,x
|
|
sta 1,x
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Apply the binary operator in a to var[x] and var[x+2]
|
|
; Valid VTL02C operators are {* + / [ ] - | ^ & < = >}
|
|
; {>} is defined as greater than _or_equal_
|
|
; An undefined operator will be interpreted as one of
|
|
; the three comparison operators
|
|
; 37 bytes
|
|
oper:
|
|
cmp #'+' ; addition operator?
|
|
beq plus
|
|
cmp #'*' ; multiplication operator?
|
|
beq mul
|
|
cmp #'/' ; division operator?
|
|
beq div
|
|
cmp #'[' ; "then" operator?
|
|
beq then_
|
|
cmp #']' ; "else" operator?
|
|
beq else_
|
|
dex ; (factored from the following ops)
|
|
cmp #'-' ; subtraction operator?
|
|
beq minus
|
|
cmp #OP_OR ; bit-wise or operator?
|
|
beq or_
|
|
cmp #'^' ; bit-wise xor operator?
|
|
beq xor_
|
|
cmp #'&' ; bit-wise and operator?
|
|
beq and_
|
|
; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
|
|
; Apply comparison operator in a to var[x] and var[x+2]
|
|
; and place result in var[x] (1: true, 0: false)
|
|
; expects: (cs), pre-decremented x
|
|
; 29 bytes
|
|
eor #'<' ; 0: '<' 1: '=' 2: '>'
|
|
sta gthan ; other values in a are undefined,
|
|
jsr minus ; but _will_ produce some result
|
|
dec gthan ; var[x] -= var[x+2]
|
|
bne oper8b ; equality test?
|
|
ora 0,x ; yes: 'or' high and low bytes
|
|
beq oper8c ; (cs) if 0
|
|
clc ; (cc) if not 0
|
|
oper8b:
|
|
lda gthan
|
|
rol
|
|
oper8c:
|
|
adc #0
|
|
and #1 ; var[x] = 1 (true), 0 (false)
|
|
oper8d:
|
|
sta 0,x
|
|
lda #0
|
|
beq minus3 ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; expects: (cs)
|
|
; 14 bytes
|
|
then_:
|
|
lda 0,x
|
|
ora 1,x
|
|
beq minus4
|
|
lda 2,x
|
|
sta 0,x
|
|
lda 3,x
|
|
bcs minus3 ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; expects: (cs)
|
|
; 10 bytes
|
|
else_:
|
|
lda 0,x
|
|
ora 1,x
|
|
beq plus
|
|
lda #0
|
|
beq oper8d ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; var[x] -= var[x+2]
|
|
; expects: (cs), pre-decremented x
|
|
; 11 bytes
|
|
minus:
|
|
jsr minus2
|
|
inx
|
|
minus2:
|
|
lda 1,x
|
|
sbc 3,x
|
|
minus3:
|
|
sta 1,x
|
|
minus4:
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; var[x] &= var[x+2]
|
|
; expects: (cs), pre-decremented x
|
|
; 10 bytes
|
|
and_:
|
|
jsr and_2
|
|
inx
|
|
and_2:
|
|
lda 1,x
|
|
and 3,x
|
|
bcs minus3 ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; var[x] |= var[x+2]
|
|
; expects: (cs), pre-decremented x
|
|
; 10 bytes
|
|
or_:
|
|
jsr or_2
|
|
inx
|
|
or_2:
|
|
lda 1,x
|
|
ora 3,x
|
|
bcs minus3 ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; var[x] ^= var[x+2]
|
|
; expects: (cs), pre-decremented x
|
|
; 10 bytes
|
|
xor_:
|
|
jsr xor_2
|
|
inx
|
|
xor_2:
|
|
lda 1,x
|
|
eor 3,x
|
|
bcs minus3 ; (always taken)
|
|
;-----------------------------------------------------;
|
|
; 16-bit unsigned division routine
|
|
; var[x] /= var[x+2], {%} = remainder, {>} modified
|
|
; var[x] /= 0 produces {%} = var[x], var[x] = 65535
|
|
; 43 bytes
|
|
div:
|
|
lda #0
|
|
sta remn ; {%} = 0
|
|
sta remn+1
|
|
lda #16
|
|
sta gthan ; {>} = loop counter
|
|
div1:
|
|
asl 0,x ; var[x] is gradually replaced
|
|
rol 1,x ; with the quotient
|
|
rol remn ; {%} is gradually replaced
|
|
rol remn+1 ; with the remainder
|
|
lda remn
|
|
cmp 2,x
|
|
lda remn+1 ; partial remainder >= var[x+2]?
|
|
sbc 3,x
|
|
bcc div2
|
|
sta remn+1 ; yes: update the partial
|
|
lda remn ; remainder and set the
|
|
sbc 2,x ; low bit in the partial
|
|
sta remn ; quotient
|
|
inc 0,x
|
|
div2:
|
|
dec gthan
|
|
bne div1 ; loop 16 times
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; If text at @[y] is a decimal constant, translate it
|
|
; into var[x] (discarding any overflow) and update y
|
|
; entry: @[y] -> text containing possible constant;
|
|
; leading space characters are skipped, but
|
|
; any spaces encountered after a conversion
|
|
; has begun will end the conversion.
|
|
; used by: user:, getval:
|
|
; uses: mul:, plus:, var[x], var[x+2], {@ > ?}
|
|
; exit: (ne): var[x] = constant, @[y] -> next text
|
|
; (eq): var[x] = 0, @[y] unchanged
|
|
; (cs): in all but the truly strangest cases
|
|
; 43 bytes
|
|
cvbin:
|
|
lda #0
|
|
sta 0,x ; var[x] = 0
|
|
sta 1,x
|
|
sta 3,x
|
|
jsr getbyte ; skip any leading spaces
|
|
sty ques ; save pointer
|
|
cvbin2:
|
|
lda (at),y ; grab a char
|
|
eor #'0' ; if char at @[y] is not a
|
|
cmp #10 ; decimal digit then stop
|
|
bcs cvbin3 ; the conversion
|
|
pha ; save decimal digit
|
|
lda #10
|
|
sta 2,x
|
|
jsr mul ; var[x] *= 10
|
|
sta 3,x
|
|
pla ; retrieve decimal digit
|
|
sta 2,x
|
|
jsr plus ; var[x] += digit
|
|
iny ; loop for more digits
|
|
bpl cvbin2 ; (with safety escape)
|
|
cvbin3:
|
|
cpy ques ; (ne) if valid, (eq) if not
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Accept input line from user and store it in linbuf,
|
|
; zero-terminated (allows very primitive edit/cancel)
|
|
; entry: (jsr to inln or newln, not inln6)
|
|
; used by: user:, getval:
|
|
; uses: inch:, outnl:, linbuf, {@}
|
|
; exit: @[y] -> linbuf
|
|
; 42 bytes
|
|
inln6:
|
|
cmp #ESC ; escape?
|
|
beq newln ; yes: discard entire line
|
|
iny ; line limit exceeded?
|
|
bpl inln2 ; no: keep going
|
|
newln:
|
|
jsr outnl ; yes: discard entire line
|
|
inln:
|
|
ldy #<linbuf ; entry point: start a fresh line
|
|
sty at ; {@} -> input line buffer
|
|
ldy #>linbuf
|
|
sty at+1
|
|
ldy #1
|
|
inln5:
|
|
dey
|
|
bmi newln
|
|
inln2:
|
|
jsr inch ; get (and echo) one key press
|
|
cmp #BS ; backspace?
|
|
beq inln5 ; yes: delete previous char
|
|
cmp #$0d ; cr?
|
|
bne inln3
|
|
lda #0 ; yes: replace with null
|
|
inln3:
|
|
sta (at),y ; put key in linbuf
|
|
bne inln6 ; continue if not null
|
|
tay ; y = 0
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Find the first/next stored program line >= {#}
|
|
; entry: (cc): start search at program beginning
|
|
; (cs): start search at next line
|
|
; ({@} -> beginning of current line)
|
|
; used by: skp2:, findln:
|
|
; uses: prgm, {@ # & (}
|
|
; exit: (cs): {@}, x:a and {(} undefined, y = 2
|
|
; (cc): {@} -> beginning of found line, y = 2,
|
|
; x:a = {(} = actual found line number
|
|
; 62 bytes
|
|
find:
|
|
ldx #>prgm
|
|
lda #<prgm
|
|
bcc find1st ; cc: search begins at first line
|
|
ldx at+1
|
|
ldy #2
|
|
findnxt:
|
|
lda at
|
|
cmp ampr
|
|
lda at+1
|
|
sbc ampr+1 ; {@} >= {&} (end of program)?
|
|
bcs findrts ; yes: search failed (cs)
|
|
find3:
|
|
lda at
|
|
adc (at),y ; no: {@} -> next line
|
|
bcc find5
|
|
inx
|
|
find1st:
|
|
stx at+1
|
|
find5:
|
|
sta at
|
|
ldy #0
|
|
lda (at),y
|
|
sta lparen ; {(} = current line number
|
|
cmp pound ; (invalid if {@} >= {&}, but
|
|
iny ; we'll catch that later...)
|
|
lda (at),y
|
|
sta lparen+1
|
|
sbc pound+1 ; if {(} < {#} then try the next
|
|
iny ; program line
|
|
bcc findnxt
|
|
lda at ; {@} >= {&} (end of program)?
|
|
cmp ampr ; yes: search failed (cs)
|
|
lda at+1 ; no: search succeeded (cc)
|
|
sbc ampr+1
|
|
lda lparen
|
|
ldx lparen+1
|
|
findrts:
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Fetch a byte at @[y], ignoring space characters
|
|
; 10 bytes
|
|
skpbyte:
|
|
iny ; skip over current char
|
|
getbyte:
|
|
lda (at),y
|
|
beq getbyt2
|
|
cmp #' '
|
|
beq skpbyte ; skip over any space char(s)
|
|
getbyt2:
|
|
rts
|
|
;-----------------------------------------------------;
|
|
; Check for user keypress and return with (cc) if none
|
|
; is pending. Otherwise, fall through to inch
|
|
; and return with (cs).
|
|
; 6 bytes
|
|
inkey:
|
|
;lda KBD ; is there a keypress waiting?
|
|
;asl
|
|
;bcc outrts ; no: return with (cc)
|
|
lda serialRaw ; [Gigatron] is there a keypress?
|
|
cmp #255 ; [Gigatron]
|
|
beq outrts ; [Gigatron] no: return with (eq)
|
|
; [Gigatron] fall into inch and wait for a *second* key
|
|
; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
|
|
; Read key from stdin into a, echo, (cs)
|
|
; drop stack and abort to "OK" prompt if ctrl-C
|
|
; 16 bytes
|
|
inch:
|
|
sty dolr ; save y reg
|
|
;jsr KEYIN ; get a char from keyboard
|
|
lda #0 ; [Gigatron]
|
|
brk ; [Gigatron] get char from keyboard
|
|
ldy dolr ; restore y reg
|
|
;and #$7f ; strip apple's hi-bit
|
|
cmp #$03 ; ctrl-C?
|
|
bne outch ; no: echo to terminal
|
|
jmp start ; yes: abort to "OK" prompt
|
|
; - - - - - - - - - - - - - - - - - - - - - - - - - - ;
|
|
; Print ASCII char in a to stdout, (cs)
|
|
; 9 bytes
|
|
outch:
|
|
pha ; save original char
|
|
ora #$80 ; apples prefer "high" ASCII
|
|
;jsr COUT ; emit char via apple monitor
|
|
brk ; [Gigatron] system call for output
|
|
pla ; restore original char
|
|
sec ; (by contract with callers)
|
|
outrts:
|
|
rts
|
|
;-----------------------------------------------------;
|