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

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* In some cases, bits would be dropped when writing if there wasn't enough space in the buffer.
* Fixes bad hunk maps being written to CHD files and incorrect hunk map data being read.
This commit is contained in:
987123879113 2024-02-24 00:44:57 +09:00 committed by Vas Crabb
parent a1cb730d16
commit 0b15781e69
1 changed files with 45 additions and 13 deletions
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58
src/lib/util/bitstream.h
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@ -40,10 +40,11 @@ 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
};
@ -64,7 +65,7 @@ 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
@ -85,7 +86,8 @@ 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_dlength(srclength),
m_dbitoffs(0)
{
}
@ -103,12 +105,31 @@ inline uint32_t bitstream_in::peek(int numbits)
// fetch data if we need more
if (numbits > m_bits)
{
while (m_bits <= 24)
while (m_bits < 32)
{
uint32_t newbits = 0;
if (m_doffset < m_dlength)
m_buffer |= m_read[m_doffset] << (24 - m_bits);
m_doffset++;
m_bits += 8;
{
// 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++;
}
}
}
@ -196,8 +217,11 @@ 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
if (m_bits + numbits > 32)
while (m_bits + numbits >= 32 && numbits > 0)
{
while (m_bits >= 8)
{
if (m_doffset < m_dlength)
@ -207,11 +231,19 @@ inline void bitstream_out::write(uint32_t newbits, int numbits)
m_bits -= 8;
}
// shift the bits to the top
if (numbits == 0)
newbits = 0;
else
newbits <<= 32 - numbits;
// 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;
// now shift it down to account for the number of bits we already have and OR them in
m_buffer |= newbits >> m_bits;