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z8: Fix calculation of half carry flag. Z8671 BASIC no longer prints "12" when the result is 18.

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This commit is contained in:
AJR 2019-07-08 02:01:43 -04:00
parent 765b5844a7
commit f4edc801bc
1 changed files with 8 additions and 6 deletions
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14
src/devices/cpu/z8/z8ops.hxx
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@ -245,7 +245,8 @@ void z8_device::add_carry(uint8_t dst, uint8_t src)
{
/* dst <- dst + src + C */
uint8_t data = register_read(dst);
uint16_t new_data = data + src + flag(C);
uint8_t c = flag(C) ? 1 : 0;
uint16_t new_data = data + src + c;
set_flag_c(new_data & 0x100);
new_data &= 0xff;
@ -253,7 +254,7 @@ void z8_device::add_carry(uint8_t dst, uint8_t src)
set_flag_s(new_data & 0x80);
set_flag_v(((data & 0x80) == (src & 0x80)) && ((new_data & 0x80) != (src & 0x80)));
set_flag_d(0);
set_flag_h(((data & 0x1f) == 0x0f) && ((new_data & 0x1f) == 0x10));
set_flag_h((data & 0x0f) + (src & 0x0f) + c >= 0x10);
register_write(dst, new_data);
}
@ -277,7 +278,7 @@ void z8_device::add(uint8_t dst, uint8_t src)
set_flag_s(new_data & 0x80);
set_flag_v(((data & 0x80) == (src & 0x80)) && ((new_data & 0x80) != (src & 0x80)));
set_flag_d(0);
set_flag_h(((data & 0x1f) == 0x0f) && ((new_data & 0x1f) == 0x10));
set_flag_h((data & 0x0f) + (src & 0x0f) >= 0x10);
register_write(dst, new_data);
}
@ -400,7 +401,8 @@ void z8_device::subtract_carry(uint8_t dst, uint8_t src)
{
/* dst <- dst - src - C */
uint8_t data = register_read(dst);
uint16_t new_data = data - src - flag(C);
uint8_t c = flag(C) ? 1 : 0;
uint16_t new_data = data - src - c;
set_flag_c(new_data & 0x100);
new_data &= 0xff;
@ -408,7 +410,7 @@ void z8_device::subtract_carry(uint8_t dst, uint8_t src)
set_flag_s(new_data & 0x80);
set_flag_v(((data & 0x80) != (src & 0x80)) && ((new_data & 0x80) == (src & 0x80)));
set_flag_d(1);
set_flag_h(!(((data & 0x1f) == 0x0f) && ((new_data & 0x1f) == 0x10)));
set_flag_h((data & 0x0f) < (src & 0x0f) + c);
register_write(dst, new_data);
}
@ -432,7 +434,7 @@ void z8_device::subtract(uint8_t dst, uint8_t src)
set_flag_s(new_data & 0x80);
set_flag_v(((data & 0x80) != (src & 0x80)) && ((new_data & 0x80) == (src & 0x80)));
set_flag_d(1);
set_flag_h(!(((data & 0x1f) == 0x0f) && ((new_data & 0x1f) == 0x10)));
set_flag_h((data & 0x0f) < (src & 0x0f));
register_write(dst, new_data);
}