diff options
Diffstat (limited to 'deps/libchdr/src/libchdr_bitstream.c')
-rw-r--r-- | deps/libchdr/src/libchdr_bitstream.c | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/deps/libchdr/src/libchdr_bitstream.c b/deps/libchdr/src/libchdr_bitstream.c new file mode 100644 index 0000000..c82a67d --- /dev/null +++ b/deps/libchdr/src/libchdr_bitstream.c @@ -0,0 +1,125 @@ +/* license:BSD-3-Clause + * copyright-holders:Aaron Giles +*************************************************************************** + + bitstream.c + + Helper classes for reading/writing at the bit level. + +***************************************************************************/ + +#include <stdlib.h> +#include <libchdr/bitstream.h> + +/*************************************************************************** + * INLINE FUNCTIONS + *************************************************************************** + */ + +int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); } + +/*------------------------------------------------- + * create_bitstream - constructor + *------------------------------------------------- + */ + +struct bitstream* create_bitstream(const void *src, uint32_t srclength) +{ + struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream)); + bitstream->buffer = 0; + bitstream->bits = 0; + bitstream->read = (const uint8_t*)src; + bitstream->doffset = 0; + bitstream->dlength = srclength; + return bitstream; +} + + +/*----------------------------------------------------- + * bitstream_peek - fetch the requested number of bits + * but don't advance the input pointer + *----------------------------------------------------- + */ + +uint32_t bitstream_peek(struct bitstream* bitstream, int numbits) +{ + if (numbits == 0) + return 0; + + /* fetch data if we need more */ + if (numbits > bitstream->bits) + { + while (bitstream->bits <= 24) + { + if (bitstream->doffset < bitstream->dlength) + bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits); + bitstream->doffset++; + bitstream->bits += 8; + } + } + + /* return the data */ + return bitstream->buffer >> (32 - numbits); +} + + +/*----------------------------------------------------- + * bitstream_remove - advance the input pointer by the + * specified number of bits + *----------------------------------------------------- + */ + +void bitstream_remove(struct bitstream* bitstream, int numbits) +{ + bitstream->buffer <<= numbits; + bitstream->bits -= numbits; +} + + +/*----------------------------------------------------- + * bitstream_read - fetch the requested number of bits + *----------------------------------------------------- + */ + +uint32_t bitstream_read(struct bitstream* bitstream, int numbits) +{ + uint32_t result = bitstream_peek(bitstream, numbits); + bitstream_remove(bitstream, numbits); + return result; +} + + +/*------------------------------------------------- + * read_offset - return the current read offset + *------------------------------------------------- + */ + +uint32_t bitstream_read_offset(struct bitstream* bitstream) +{ + uint32_t result = bitstream->doffset; + int bits = bitstream->bits; + while (bits >= 8) + { + result--; + bits -= 8; + } + return result; +} + + +/*------------------------------------------------- + * flush - flush to the nearest byte + *------------------------------------------------- + */ + +uint32_t bitstream_flush(struct bitstream* bitstream) +{ + while (bitstream->bits >= 8) + { + bitstream->doffset--; + bitstream->bits -= 8; + } + bitstream->bits = bitstream->buffer = 0; + return bitstream->doffset; +} + |