88 lines
2.1 KiB
C
88 lines
2.1 KiB
C
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/*
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* decin.c
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*
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* Decoder inputting of compressed data
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*/
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#include "decoder.h"
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/*
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* Initialises the bit buffer state
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*/
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void NEAR initialise_decoder_bitbuf(t_decoder_context *context)
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{
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byte *p;
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/*
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* If we're decoding an uncompressed block, don't use the
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* bit buffer; we're reading directly out of the input.
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*/
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if (context->dec_block_type == BLOCKTYPE_UNCOMPRESSED)
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return;
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if ((context->dec_input_curpos + sizeof(ulong)) > context->dec_end_input_pos)
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return;
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p = context->dec_input_curpos;
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context->dec_bitbuf =
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((ulong) p[2] | (((ulong) p[3]) << 8)) |
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((((ulong) p[0] | (((ulong) p[1]) << 8))) << 16);
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context->dec_bitcount = 16;
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context->dec_input_curpos += 4;
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}
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/*
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* Initialise input buffer and bitwise i/o
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*/
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void NEAR init_decoder_input(t_decoder_context *context)
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{
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initialise_decoder_bitbuf(context);
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}
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void NEAR fillbuf(t_decoder_context *context, int n)
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{
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context->dec_bitbuf <<= n;
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context->dec_bitcount -= (char)n;
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if (context->dec_bitcount <= 0)
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{
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if (context->dec_input_curpos >= context->dec_end_input_pos)
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{
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context->dec_error_condition = true;
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return;
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}
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context->dec_bitbuf |= ((((ulong) *context->dec_input_curpos | (((ulong) *(context->dec_input_curpos+1)) << 8))) << (-context->dec_bitcount));
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context->dec_input_curpos += 2;
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context->dec_bitcount += 16;
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if (context->dec_bitcount <= 0)
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{
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if (context->dec_input_curpos >= context->dec_end_input_pos)
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{
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context->dec_error_condition = true;
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return;
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}
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context->dec_bitbuf |= ((((ulong) *context->dec_input_curpos | (((ulong) *(context->dec_input_curpos+1)) << 8))) << (-context->dec_bitcount));
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context->dec_input_curpos += 2;
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context->dec_bitcount += 16;
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}
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}
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}
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ulong NEAR getbits(t_decoder_context *context, int n)
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{
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ulong value;
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value = context->dec_bitbuf >> (32-(n));
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fillbuf(context, n);
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return value;
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}
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