222 lines
7 KiB
C
222 lines
7 KiB
C
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/*
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* decblk.c
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*
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* main decoder module
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*/
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#include "decoder.h"
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#include <memory.h>
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#pragma intrinsic(memcpy)
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/*
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* Decode a block type
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*/
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static int decode_block(
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t_decoder_context *context,
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lzx_block_type block_type,
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long bufpos,
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long amount_to_decode
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)
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{
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int result;
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if (block_type == BLOCKTYPE_ALIGNED)
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result = decode_aligned_offset_block(context, bufpos, (int) amount_to_decode);
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else if (block_type == BLOCKTYPE_VERBATIM)
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result = decode_verbatim_block(context, bufpos, (int) amount_to_decode);
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else if (block_type == BLOCKTYPE_UNCOMPRESSED)
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result = decode_uncompressed_block(context, bufpos, (int) amount_to_decode);
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else /* no other block types exist */
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result = -1;
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return result;
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}
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/*
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* Main decode entrypoint
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*/
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long NEAR decode_data(t_decoder_context *context, long bytes_to_decode)
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{
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ulong amount_can_decode;
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long total_decoded;
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total_decoded = 0;
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while (bytes_to_decode > 0)
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{
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if (context->dec_decoder_state == DEC_STATE_START_NEW_BLOCK)
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{
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ulong temp1;
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ulong temp2;
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ulong temp3;
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bool do_translation;
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/*
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* If this is the first time this group, then get the
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* file size for translation.
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*/
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if (context->dec_first_time_this_group)
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{
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context->dec_first_time_this_group = false;
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do_translation = (bool) getbits(context, 1);
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if (do_translation)
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{
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ulong high, low;
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high = getbits(context, 16);
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low = getbits(context, 16);
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context->dec_current_file_size = (high<<16)|low;
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}
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else
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{
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context->dec_current_file_size = 0;
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}
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}
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/*
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* If the last block we decoded was uncompressed, then
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* we need to skip the pad byte (if it exists), and
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* initialise the decoder's bit buffer
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*/
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if (context->dec_block_type == BLOCKTYPE_UNCOMPRESSED)
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{
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/*
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* If block size was odd, a pad byte is required
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*/
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if (context->dec_original_block_size & 1)
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{
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if (context->dec_input_curpos < context->dec_end_input_pos)
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context->dec_input_curpos++;
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}
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/* so that initialise_decoder_bitbuf() will succeed */
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context->dec_block_type = BLOCKTYPE_INVALID;
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initialise_decoder_bitbuf(context);
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}
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/* get the block type */
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context->dec_block_type = (lzx_block_type) getbits(context, 3);
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/* get size of block (in uncompressed bytes) to decode */
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temp1 = getbits(context, 8);
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temp2 = getbits(context, 8);
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temp3 = getbits(context, 8);
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/*
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* How large is the block we're going to decode?
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* It can be from 0...16777215 bytes (16MB)
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*/
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context->dec_block_size =
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context->dec_original_block_size = (temp1<<16) + (temp2<<8) + (temp3);
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/* if block is an aligned type, read the aligned offset tree */
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if (context->dec_block_type == BLOCKTYPE_ALIGNED)
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read_aligned_offset_tree(context);
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/* read trees */
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if (context->dec_block_type == BLOCKTYPE_VERBATIM ||
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context->dec_block_type == BLOCKTYPE_ALIGNED)
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{
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/* backup old trees */
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memcpy(
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context->dec_main_tree_prev_len,
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context->dec_main_tree_len,
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MAIN_TREE_ELEMENTS
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);
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memcpy(
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context->dec_secondary_length_tree_prev_len,
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context->dec_secondary_length_tree_len,
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NUM_SECONDARY_LENGTHS
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);
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read_main_and_secondary_trees(context);
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}
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else if (context->dec_block_type == BLOCKTYPE_UNCOMPRESSED)
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{
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if (handle_beginning_of_uncompressed_block(context) == false)
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return -1;
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}
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else
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{
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/* no other block types are supported at this time */
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return -1;
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}
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context->dec_decoder_state = DEC_STATE_DECODING_DATA;
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}
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/*
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* Keep decoding until the whole block has been decoded
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*/
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while ((context->dec_block_size > 0) && (bytes_to_decode > 0))
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{
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int decode_residue;
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amount_can_decode = min(context->dec_block_size, bytes_to_decode);
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/* shouldn't happen */
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if (amount_can_decode == 0)
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return -1;
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decode_residue = decode_block(
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context,
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context->dec_block_type,
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context->dec_bufpos,
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amount_can_decode
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);
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/*
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* We should have decoded exactly the amount we wanted,
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* since the encoder makes sure that no matches span 32K
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* boundaries.
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*
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* If the data was corrupted, it's possible that we decoded
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* up to MAX_MATCH bytes more than we wanted to.
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*/
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if (decode_residue != 0)
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{
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/* error, we didn't decode what we wanted! */
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return -1;
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}
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context->dec_block_size -= amount_can_decode;
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bytes_to_decode -= amount_can_decode;
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total_decoded += amount_can_decode;
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}
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if (context->dec_block_size == 0)
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{
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context->dec_decoder_state = DEC_STATE_START_NEW_BLOCK;
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}
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if (bytes_to_decode == 0)
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{
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initialise_decoder_bitbuf(context);
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}
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}
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#ifdef BIT16
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copy_data_to_output(
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context,
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total_decoded,
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context->dec_output_buffer
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);
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#else
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copy_data_to_output(
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context,
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total_decoded,
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context->dec_bufpos ?
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&context->dec_mem_window[context->dec_bufpos - total_decoded] :
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&context->dec_mem_window[context->dec_window_size - total_decoded]
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);
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#endif
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return total_decoded;
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}
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