mirror of
https://github.com/RetroDECK/Duckstation.git
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126 lines
3.1 KiB
C
126 lines
3.1 KiB
C
/* license:BSD-3-Clause
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* copyright-holders:Aaron Giles
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***************************************************************************
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bitstream.c
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Helper classes for reading/writing at the bit level.
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***************************************************************************/
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#include <stdlib.h>
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#include <libchdr/bitstream.h>
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/***************************************************************************
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* INLINE FUNCTIONS
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***************************************************************************
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*/
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int bitstream_overflow(struct bitstream* bitstream) { return ((bitstream->doffset - bitstream->bits / 8) > bitstream->dlength); }
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/*-------------------------------------------------
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* create_bitstream - constructor
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*-------------------------------------------------
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*/
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struct bitstream* create_bitstream(const void *src, uint32_t srclength)
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{
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struct bitstream* bitstream = (struct bitstream*)malloc(sizeof(struct bitstream));
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bitstream->buffer = 0;
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bitstream->bits = 0;
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bitstream->read = (const uint8_t*)src;
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bitstream->doffset = 0;
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bitstream->dlength = srclength;
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return bitstream;
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}
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/*-----------------------------------------------------
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* bitstream_peek - fetch the requested number of bits
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* but don't advance the input pointer
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*-----------------------------------------------------
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*/
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uint32_t bitstream_peek(struct bitstream* bitstream, int numbits)
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{
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if (numbits == 0)
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return 0;
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/* fetch data if we need more */
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if (numbits > bitstream->bits)
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{
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while (bitstream->bits <= 24)
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{
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if (bitstream->doffset < bitstream->dlength)
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bitstream->buffer |= bitstream->read[bitstream->doffset] << (24 - bitstream->bits);
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bitstream->doffset++;
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bitstream->bits += 8;
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}
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}
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/* return the data */
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return bitstream->buffer >> (32 - numbits);
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}
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/*-----------------------------------------------------
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* bitstream_remove - advance the input pointer by the
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* specified number of bits
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*-----------------------------------------------------
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*/
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void bitstream_remove(struct bitstream* bitstream, int numbits)
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{
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bitstream->buffer <<= numbits;
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bitstream->bits -= numbits;
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}
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/*-----------------------------------------------------
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* bitstream_read - fetch the requested number of bits
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*-----------------------------------------------------
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*/
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uint32_t bitstream_read(struct bitstream* bitstream, int numbits)
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{
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uint32_t result = bitstream_peek(bitstream, numbits);
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bitstream_remove(bitstream, numbits);
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return result;
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}
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/*-------------------------------------------------
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* read_offset - return the current read offset
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*-------------------------------------------------
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*/
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uint32_t bitstream_read_offset(struct bitstream* bitstream)
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{
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uint32_t result = bitstream->doffset;
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int bits = bitstream->bits;
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while (bits >= 8)
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{
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result--;
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bits -= 8;
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}
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return result;
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}
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/*-------------------------------------------------
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* flush - flush to the nearest byte
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*-------------------------------------------------
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*/
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uint32_t bitstream_flush(struct bitstream* bitstream)
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{
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while (bitstream->bits >= 8)
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{
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bitstream->doffset--;
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bitstream->bits -= 8;
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}
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bitstream->bits = bitstream->buffer = 0;
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return bitstream->doffset;
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}
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