зеркало из https://github.com/mozilla/mozjpeg.git
147 строки
3.5 KiB
C
147 строки
3.5 KiB
C
/*
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* jdmcu.c
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*
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* Copyright (C) 1991, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains MCU disassembly routines and quantization descaling.
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* These routines are invoked via the disassemble_MCU and
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* disassemble_init/term methods.
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*/
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#include "jinclude.h"
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/*
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* Quantization descaling and zigzag reordering
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*/
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/* ZAG[i] is the natural-order position of the i'th element of zigzag order. */
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static const short ZAG[DCTSIZE2] = {
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0, 1, 8, 16, 9, 2, 3, 10,
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17, 24, 32, 25, 18, 11, 4, 5,
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12, 19, 26, 33, 40, 48, 41, 34,
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27, 20, 13, 6, 7, 14, 21, 28,
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35, 42, 49, 56, 57, 50, 43, 36,
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29, 22, 15, 23, 30, 37, 44, 51,
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58, 59, 52, 45, 38, 31, 39, 46,
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53, 60, 61, 54, 47, 55, 62, 63
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};
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LOCAL void
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qdescale_zig (JBLOCK input, JBLOCKROW outputptr, QUANT_TBL_PTR quanttbl)
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{
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short i;
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for (i = 0; i < DCTSIZE2; i++) {
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(*outputptr)[ZAG[i]] = (*input++) * (*quanttbl++);
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}
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}
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/*
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* Fetch one MCU row from entropy_decode, build coefficient array.
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* This version is used for noninterleaved (single-component) scans.
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*/
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METHODDEF void
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disassemble_noninterleaved_MCU (decompress_info_ptr cinfo,
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JBLOCKIMAGE image_data)
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{
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JBLOCK MCU_data[1];
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long mcuindex;
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jpeg_component_info * compptr;
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QUANT_TBL_PTR quant_ptr;
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/* this is pretty easy since there is one component and one block per MCU */
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compptr = cinfo->cur_comp_info[0];
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quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
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for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
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/* Fetch the coefficient data */
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(*cinfo->methods->entropy_decode) (cinfo, MCU_data);
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/* Descale, reorder, and distribute it into the image array */
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qdescale_zig(MCU_data[0], image_data[0][0] + mcuindex, quant_ptr);
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}
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}
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/*
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* Fetch one MCU row from entropy_decode, build coefficient array.
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* This version is used for interleaved (multi-component) scans.
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*/
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METHODDEF void
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disassemble_interleaved_MCU (decompress_info_ptr cinfo,
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JBLOCKIMAGE image_data)
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{
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JBLOCK MCU_data[MAX_BLOCKS_IN_MCU];
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long mcuindex;
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short blkn, ci, xpos, ypos;
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jpeg_component_info * compptr;
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QUANT_TBL_PTR quant_ptr;
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JBLOCKROW image_ptr;
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for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) {
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/* Fetch the coefficient data */
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(*cinfo->methods->entropy_decode) (cinfo, MCU_data);
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/* Descale, reorder, and distribute it into the image array */
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blkn = 0;
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for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
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compptr = cinfo->cur_comp_info[ci];
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quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
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for (ypos = 0; ypos < compptr->MCU_height; ypos++) {
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image_ptr = image_data[ci][ypos] + (mcuindex * compptr->MCU_width);
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for (xpos = 0; xpos < compptr->MCU_width; xpos++) {
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qdescale_zig(MCU_data[blkn], image_ptr, quant_ptr);
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image_ptr++;
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blkn++;
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}
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}
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}
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}
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}
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/*
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* Initialize for processing a scan.
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*/
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METHODDEF void
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disassemble_init (decompress_info_ptr cinfo)
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{
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/* no work for now */
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}
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/*
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* Clean up after a scan.
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*/
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METHODDEF void
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disassemble_term (decompress_info_ptr cinfo)
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{
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/* no work for now */
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}
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/*
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* The method selection routine for MCU disassembly.
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*/
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GLOBAL void
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jseldmcu (decompress_info_ptr cinfo)
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{
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if (cinfo->comps_in_scan == 1)
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cinfo->methods->disassemble_MCU = disassemble_noninterleaved_MCU;
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else
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cinfo->methods->disassemble_MCU = disassemble_interleaved_MCU;
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cinfo->methods->disassemble_init = disassemble_init;
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cinfo->methods->disassemble_term = disassemble_term;
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}
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