| /* |
| * jdmcu.c |
| * |
| * Copyright (C) 1991, 1992, Thomas G. Lane. |
| * This file is part of the Independent JPEG Group's software. |
| * For conditions of distribution and use, see the accompanying README file. |
| * |
| * This file contains MCU disassembly routines and quantization descaling. |
| * These routines are invoked via the disassemble_MCU, reverse_DCT, and |
| * disassemble_init/term methods. |
| */ |
| |
| #include "jinclude.h" |
| |
| |
| /* |
| * Quantization descaling and zigzag reordering |
| */ |
| |
| |
| /* ZAG[i] is the natural-order position of the i'th element of zigzag order. */ |
| |
| static const short ZAG[DCTSIZE2] = { |
| 0, 1, 8, 16, 9, 2, 3, 10, |
| 17, 24, 32, 25, 18, 11, 4, 5, |
| 12, 19, 26, 33, 40, 48, 41, 34, |
| 27, 20, 13, 6, 7, 14, 21, 28, |
| 35, 42, 49, 56, 57, 50, 43, 36, |
| 29, 22, 15, 23, 30, 37, 44, 51, |
| 58, 59, 52, 45, 38, 31, 39, 46, |
| 53, 60, 61, 54, 47, 55, 62, 63 |
| }; |
| |
| |
| LOCAL void |
| qdescale_zig (JBLOCK input, JBLOCKROW outputptr, QUANT_TBL_PTR quanttbl) |
| { |
| const short * zagptr = ZAG; |
| short i; |
| |
| for (i = DCTSIZE2-1; i >= 0; i--) { |
| (*outputptr)[*zagptr++] = (*input++) * (*quanttbl++); |
| } |
| } |
| |
| |
| |
| /* |
| * Fetch one MCU row from entropy_decode, build coefficient array. |
| * This version is used for noninterleaved (single-component) scans. |
| */ |
| |
| METHODDEF void |
| disassemble_noninterleaved_MCU (decompress_info_ptr cinfo, |
| JBLOCKIMAGE image_data) |
| { |
| JBLOCK MCU_data[1]; |
| long mcuindex; |
| jpeg_component_info * compptr; |
| QUANT_TBL_PTR quant_ptr; |
| |
| /* this is pretty easy since there is one component and one block per MCU */ |
| compptr = cinfo->cur_comp_info[0]; |
| quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no]; |
| for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) { |
| /* Fetch the coefficient data */ |
| (*cinfo->methods->entropy_decode) (cinfo, MCU_data); |
| /* Descale, reorder, and distribute it into the image array */ |
| qdescale_zig(MCU_data[0], image_data[0][0] + mcuindex, quant_ptr); |
| } |
| } |
| |
| |
| /* |
| * Fetch one MCU row from entropy_decode, build coefficient array. |
| * This version is used for interleaved (multi-component) scans. |
| */ |
| |
| METHODDEF void |
| disassemble_interleaved_MCU (decompress_info_ptr cinfo, |
| JBLOCKIMAGE image_data) |
| { |
| JBLOCK MCU_data[MAX_BLOCKS_IN_MCU]; |
| long mcuindex; |
| short blkn, ci, xpos, ypos; |
| jpeg_component_info * compptr; |
| QUANT_TBL_PTR quant_ptr; |
| JBLOCKROW image_ptr; |
| |
| for (mcuindex = 0; mcuindex < cinfo->MCUs_per_row; mcuindex++) { |
| /* Fetch the coefficient data */ |
| (*cinfo->methods->entropy_decode) (cinfo, MCU_data); |
| /* Descale, reorder, and distribute it into the image array */ |
| blkn = 0; |
| for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
| compptr = cinfo->cur_comp_info[ci]; |
| quant_ptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no]; |
| for (ypos = 0; ypos < compptr->MCU_height; ypos++) { |
| image_ptr = image_data[ci][ypos] + (mcuindex * compptr->MCU_width); |
| for (xpos = 0; xpos < compptr->MCU_width; xpos++) { |
| qdescale_zig(MCU_data[blkn], image_ptr, quant_ptr); |
| image_ptr++; |
| blkn++; |
| } |
| } |
| } |
| } |
| } |
| |
| |
| /* |
| * Perform inverse DCT on each block in an MCU row's worth of data; |
| * output the results into a sample array starting at row start_row. |
| * NB: start_row can only be nonzero when dealing with a single-component |
| * scan; otherwise we'd have to pass different offsets for different |
| * components, since the heights of interleaved MCU rows can vary. |
| * But the pipeline controller logic is such that this is not necessary. |
| */ |
| |
| METHODDEF void |
| reverse_DCT (decompress_info_ptr cinfo, |
| JBLOCKIMAGE coeff_data, JSAMPIMAGE output_data, int start_row) |
| { |
| DCTBLOCK block; |
| JBLOCKROW browptr; |
| JSAMPARRAY srowptr; |
| long blocksperrow, bi; |
| short numrows, ri; |
| short ci; |
| |
| for (ci = 0; ci < cinfo->comps_in_scan; ci++) { |
| /* calculate size of an MCU row in this component */ |
| blocksperrow = cinfo->cur_comp_info[ci]->subsampled_width / DCTSIZE; |
| numrows = cinfo->cur_comp_info[ci]->MCU_height; |
| /* iterate through all blocks in MCU row */ |
| for (ri = 0; ri < numrows; ri++) { |
| browptr = coeff_data[ci][ri]; |
| srowptr = output_data[ci] + (ri * DCTSIZE + start_row); |
| for (bi = 0; bi < blocksperrow; bi++) { |
| /* copy the data into a local DCTBLOCK. This allows for change of |
| * representation (if DCTELEM != JCOEF). On 80x86 machines it also |
| * brings the data back from FAR storage to NEAR storage. |
| */ |
| { register JCOEFPTR elemptr = browptr[bi]; |
| register DCTELEM *localblkptr = block; |
| register short elem = DCTSIZE2; |
| |
| while (--elem >= 0) |
| *localblkptr++ = (DCTELEM) *elemptr++; |
| } |
| |
| j_rev_dct(block); /* perform inverse DCT */ |
| |
| /* output the data into the sample array. |
| * Note change from signed to unsigned representation: |
| * DCT calculation works with values +-CENTERJSAMPLE, |
| * but sample arrays always hold 0..MAXJSAMPLE. |
| * Have to do explicit range-limiting because of quantization errors |
| * and so forth in the DCT/IDCT phase. |
| */ |
| { register JSAMPROW elemptr; |
| register DCTELEM *localblkptr = block; |
| register short elemr, elemc; |
| register DCTELEM temp; |
| |
| for (elemr = 0; elemr < DCTSIZE; elemr++) { |
| elemptr = srowptr[elemr] + (bi * DCTSIZE); |
| for (elemc = 0; elemc < DCTSIZE; elemc++) { |
| temp = (*localblkptr++) + CENTERJSAMPLE; |
| if (temp < 0) temp = 0; |
| else if (temp > MAXJSAMPLE) temp = MAXJSAMPLE; |
| *elemptr++ = (JSAMPLE) temp; |
| } |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| |
| /* |
| * Initialize for processing a scan. |
| */ |
| |
| METHODDEF void |
| disassemble_init (decompress_info_ptr cinfo) |
| { |
| /* no work for now */ |
| } |
| |
| |
| /* |
| * Clean up after a scan. |
| */ |
| |
| METHODDEF void |
| disassemble_term (decompress_info_ptr cinfo) |
| { |
| /* no work for now */ |
| } |
| |
| |
| |
| /* |
| * The method selection routine for MCU disassembly. |
| */ |
| |
| GLOBAL void |
| jseldmcu (decompress_info_ptr cinfo) |
| { |
| if (cinfo->comps_in_scan == 1) |
| cinfo->methods->disassemble_MCU = disassemble_noninterleaved_MCU; |
| else |
| cinfo->methods->disassemble_MCU = disassemble_interleaved_MCU; |
| cinfo->methods->reverse_DCT = reverse_DCT; |
| cinfo->methods->disassemble_init = disassemble_init; |
| cinfo->methods->disassemble_term = disassemble_term; |
| } |