mirror of
https://github.com/jmarshall23/CnC_Remastered_Collection.git
synced 2026-08-12 08:00:55 +02:00
Justin Marshall
126 lines
2.3 KiB
C
126 lines
2.3 KiB
C
/*
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libsmacker - A C library for decoding .smk Smacker Video files
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Copyright (C) 2012-2013 Greg Kennedy
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See smacker.h for more information.
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smk_bitstream.c
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Implements a bitstream structure, which can extract and
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return a bit at a time from a raw block of bytes.
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*/
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#include "smk_bitstream.h"
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/* malloc and friends */
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#include "smk_malloc.h"
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/* BITSTREAM Functions */
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struct smk_bit_t *smk_bs_init(unsigned char *b, const unsigned long size)
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{
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struct smk_bit_t *ret = NULL;
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smk_null_check(b);
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/* allocate a bitstream struct */
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smk_malloc(ret,sizeof(struct smk_bit_t));
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/* set up the pointer to bitstream, and the size counter */
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ret->bitstream = b;
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ret->size = size;
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/* point to initial byte */
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ret->byte_num = -1;
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ret->bit_num = 7;
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/* either way NULL is returned : ) */
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error:
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return ret;
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}
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/* returns "enough bits left for a byte?" */
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static char smk_bs_query_8(struct smk_bit_t *bs)
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{
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/* sanity check */
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smk_null_check(bs);
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return (bs->byte_num + 1 < bs->size);
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error:
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return -1;
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}
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/* returns "any bits left?" */
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static char smk_bs_query_1(struct smk_bit_t *bs)
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{
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/* sanity check */
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smk_null_check(bs)
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return (bs->bit_num < 7 || smk_bs_query_8(bs));
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error:
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return -1;
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}
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/* Reads a bit
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Returns -1 if error encountered */
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char smk_bs_read_1(struct smk_bit_t *bs)
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{
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/* sanity check */
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smk_null_check(bs);
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/* don't die when running out of bits, but signal */
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if (!smk_bs_query_1(bs))
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{
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fputs("libsmacker::smk_bs_read_1(bs) - ERROR: bitstream exhausted.\n",stderr);
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goto error;
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}
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/* advance to next bit */
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bs->bit_num ++;
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/* Out of bits in this byte: next! */
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if (bs->bit_num > 7)
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{
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bs->byte_num ++;
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bs->bit_num = 0;
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}
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return (((bs->bitstream[bs->byte_num]) & (0x01 << bs->bit_num)) != 0);
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error:
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return -1;
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}
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/* Reads a byte
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Returns -1 if error. */
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short smk_bs_read_8(struct smk_bit_t *bs)
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{
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unsigned char ret = 0, i;
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/* sanity check */
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smk_null_check(bs);
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/* don't die when running out of bits, but signal */
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if (!smk_bs_query_8(bs))
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{
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fputs("libsmacker::smk_bs_read_8(bs) - ERROR: bitstream exhausted.\n",stderr);
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goto error;
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}
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for (i = 0; i < 8; i ++)
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{
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ret = ret >> 1;
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ret |= (smk_bs_read_1(bs) << 7);
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}
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return ret;
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error:
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return -1;
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}
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/* aligns struct to start of next byte */
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/*
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void smk_bs_align(struct smk_bit_t *bs)
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{
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bs->bit_num = 7;
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}
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*/
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