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Revert "util/bitstream.cpp: Fixed cases where bits would be dropped when reading and writing. (#12057)"

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This reverts commit 69c3cd7dab.

This causes CHD SHA1 digests to change.  Either it's buggy, or CHD SHA1
digests depend on the representation rather than the data itself.
This commit is contained in:
Vas Crabb 2024-02-24 02:56:52 +11:00
parent 69c3cd7dab
commit 229d19de63
1 changed files with 13 additions and 45 deletions
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58
src/lib/util/bitstream.h
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@ -40,11 +40,10 @@ public:
private:
// internal state
uint32_t m_buffer; // current bit accumulator
int m_bits; // number of bits in the accumulator
int m_bits; // number of bits in the accumulator
const uint8_t * m_read; // read pointer
uint32_t m_doffset; // byte offset within the data
uint32_t m_dlength; // length of the data
int m_dbitoffs; // bit offset within current read pointer
};
@ -65,7 +64,7 @@ public:
private:
// internal state
uint32_t m_buffer; // current bit accumulator
int m_bits; // number of bits in the accumulator
int m_bits; // number of bits in the accumulator
uint8_t * m_write; // write pointer
uint32_t m_doffset; // byte offset within the data
uint32_t m_dlength; // length of the data
@ -86,8 +85,7 @@ inline bitstream_in::bitstream_in(const void *src, uint32_t srclength)
m_bits(0),
m_read(reinterpret_cast<const uint8_t *>(src)),
m_doffset(0),
m_dlength(srclength),
m_dbitoffs(0)
m_dlength(srclength)
{
}
@ -105,31 +103,12 @@ inline uint32_t bitstream_in::peek(int numbits)
// fetch data if we need more
if (numbits > m_bits)
{
while (m_bits < 32)
while (m_bits <= 24)
{
uint32_t newbits = 0;
if (m_doffset < m_dlength)
{
// adjust current data to discard any previously read partial bits
newbits = (m_read[m_doffset] << m_dbitoffs) & 0xff;
}
if (m_bits + 8 > 32)
{
// take only what can be used to fill out the rest of the buffer
m_dbitoffs = 32 - m_bits;
newbits >>= 8 - m_dbitoffs;
m_buffer |= newbits;
m_bits += m_dbitoffs;
}
else
{
m_buffer |= newbits << (24 - m_bits);
m_bits += 8 - m_dbitoffs;
m_dbitoffs = 0;
m_doffset++;
}
m_buffer |= m_read[m_doffset] << (24 - m_bits);
m_doffset++;
m_bits += 8;
}
}
@ -217,11 +196,8 @@ inline bitstream_out::bitstream_out(void *dest, uint32_t destlength)
inline void bitstream_out::write(uint32_t newbits, int numbits)
{
newbits <<= 32 - numbits;
// flush the buffer if we're going to overflow it
while (m_bits + numbits >= 32 && numbits > 0)
{
if (m_bits + numbits > 32)
while (m_bits >= 8)
{
if (m_doffset < m_dlength)
@ -231,19 +207,11 @@ inline void bitstream_out::write(uint32_t newbits, int numbits)
m_bits -= 8;
}
// offload more bits if it'll still overflow the buffer
if (m_bits + numbits >= 32)
{
const int rem = std::min(32 - m_bits, numbits);
m_buffer |= newbits >> m_bits;
m_bits += rem;
newbits <<= rem;
numbits -= rem;
}
}
if (numbits <= 0)
return;
// shift the bits to the top
if (numbits == 0)
newbits = 0;
else
newbits <<= 32 - numbits;
// now shift it down to account for the number of bits we already have and OR them in
m_buffer |= newbits >> m_bits;