ref: 556618eb07d1ac6e2c629a60acd53c45d53261be
dir: /sys/src/cmd/gs/jpeg/jddctmgr.c/
/* * jddctmgr.c * * Copyright (C) 1994-1996, 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 the inverse-DCT management logic. * This code selects a particular IDCT implementation to be used, * and it performs related housekeeping chores. No code in this file * is executed per IDCT step, only during output pass setup. * * Note that the IDCT routines are responsible for performing coefficient * dequantization as well as the IDCT proper. This module sets up the * dequantization multiplier table needed by the IDCT routine. */ #define JPEG_INTERNALS #include "jinclude.h" #include "jpeglib.h" #include "jdct.h" /* Private declarations for DCT subsystem */ /* * The decompressor input side (jdinput.c) saves away the appropriate * quantization table for each component at the start of the first scan * involving that component. (This is necessary in order to correctly * decode files that reuse Q-table slots.) * When we are ready to make an output pass, the saved Q-table is converted * to a multiplier table that will actually be used by the IDCT routine. * The multiplier table contents are IDCT-method-dependent. To support * application changes in IDCT method between scans, we can remake the * multiplier tables if necessary. * In buffered-image mode, the first output pass may occur before any data * has been seen for some components, and thus before their Q-tables have * been saved away. To handle this case, multiplier tables are preset * to zeroes; the result of the IDCT will be a neutral gray level. */ /* Private subobject for this module */ typedef struct { struct jpeg_inverse_dct pub; /* public fields */ /* This array contains the IDCT method code that each multiplier table * is currently set up for, or -1 if it's not yet set up. * The actual multiplier tables are pointed to by dct_table in the * per-component comp_info structures. */ int cur_method[MAX_COMPONENTS]; } my_idct_controller; typedef my_idct_controller * my_idct_ptr; /* Allocated multiplier tables: big enough for any supported variant */ typedef union { ISLOW_MULT_TYPE islow_array[DCTSIZE2]; #ifdef DCT_IFAST_SUPPORTED IFAST_MULT_TYPE ifast_array[DCTSIZE2]; #endif #ifdef DCT_FLOAT_SUPPORTED FLOAT_MULT_TYPE float_array[DCTSIZE2]; #endif } multiplier_table; /* The current scaled-IDCT routines require ISLOW-style multiplier tables, * so be sure to compile that code if either ISLOW or SCALING is requested. */ #ifdef DCT_ISLOW_SUPPORTED #define PROVIDE_ISLOW_TABLES #else #ifdef IDCT_SCALING_SUPPORTED #define PROVIDE_ISLOW_TABLES #endif #endif /* * Prepare for an output pass. * Here we select the proper IDCT routine for each component and build * a matching multiplier table. */ METHODDEF(void) start_pass (j_decompress_ptr cinfo) { my_idct_ptr idct = (my_idct_ptr) cinfo->idct; int ci, i; jpeg_component_info *compptr; int method = 0; inverse_DCT_method_ptr method_ptr = NULL; JQUANT_TBL * qtbl; for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; ci++, compptr++) { /* Select the proper IDCT routine for this component's scaling */ switch (compptr->DCT_scaled_size) { #ifdef IDCT_SCALING_SUPPORTED case 1: method_ptr = jpeg_idct_1x1; method = JDCT_ISLOW; /* jidctred uses islow-style table */ break; case 2: method_ptr = jpeg_idct_2x2; method = JDCT_ISLOW; /* jidctred uses islow-style table */ break; case 4: method_ptr = jpeg_idct_4x4; method = JDCT_ISLOW; /* jidctred uses islow-style table */ break; #endif case DCTSIZE: switch (cinfo->dct_method) { #ifdef DCT_ISLOW_SUPPORTED case JDCT_ISLOW: method_ptr = jpeg_idct_islow; method = JDCT_ISLOW; break; #endif #ifdef DCT_IFAST_SUPPORTED case JDCT_IFAST: method_ptr = jpeg_idct_ifast; method = JDCT_IFAST; break; #endif #ifdef DCT_FLOAT_SUPPORTED case JDCT_FLOAT: method_ptr = jpeg_idct_float; method = JDCT_FLOAT; break; #endif default: ERREXIT(cinfo, JERR_NOT_COMPILED); break; } break; default: ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size); break; } idct->pub.inverse_DCT[ci] = method_ptr; /* Create multiplier table from quant table. * However, we can skip this if the component is uninteresting * or if we already built the table. Also, if no quant table * has yet been saved for the component, we leave the * multiplier table all-zero; we'll be reading zeroes from the * coefficient controller's buffer anyway. */ if (! compptr->component_needed || idct->cur_method[ci] == method) continue; qtbl = compptr->quant_table; if (qtbl == NULL) /* happens if no data yet for component */ continue; idct->cur_method[ci] = method; switch (method) { #ifdef PROVIDE_ISLOW_TABLES case JDCT_ISLOW: { /* For LL&M IDCT method, multipliers are equal to raw quantization * coefficients, but are stored as ints to ensure access efficiency. */ ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table; for (i = 0; i < DCTSIZE2; i++) { ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[i]; } } break; #endif #ifdef DCT_IFAST_SUPPORTED case JDCT_IFAST: { /* For AA&N IDCT method, multipliers are equal to quantization * coefficients scaled by scalefactor[row]*scalefactor[col], where * scalefactor[0] = 1 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7 * For integer operation, the multiplier table is to be scaled by * IFAST_SCALE_BITS. */ IFAST_MULT_TYPE * ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table; #define CONST_BITS 14 static const INT16 aanscales[DCTSIZE2] = { /* precomputed values scaled up by 14 bits */ 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520, 22725, 31521, 29692, 26722, 22725, 17855, 12299, 6270, 21407, 29692, 27969, 25172, 21407, 16819, 11585, 5906, 19266, 26722, 25172, 22654, 19266, 15137, 10426, 5315, 16384, 22725, 21407, 19266, 16384, 12873, 8867, 4520, 12873, 17855, 16819, 15137, 12873, 10114, 6967, 3552, 8867, 12299, 11585, 10426, 8867, 6967, 4799, 2446, 4520, 6270, 5906, 5315, 4520, 3552, 2446, 1247 }; SHIFT_TEMPS for (i = 0; i < DCTSIZE2; i++) { ifmtbl[i] = (IFAST_MULT_TYPE) DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[i], (INT32) aanscales[i]), CONST_BITS-IFAST_SCALE_BITS); } } break; #endif #ifdef DCT_FLOAT_SUPPORTED case JDCT_FLOAT: { /* For float AA&N IDCT method, multipliers are equal to quantization * coefficients scaled by scalefactor[row]*scalefactor[col], where * scalefactor[0] = 1 * scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7 */ FLOAT_MULT_TYPE * fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table; int row, col; static const double aanscalefactor[DCTSIZE] = { 1.0, 1.387039845, 1.306562965, 1.175875602, 1.0, 0.785694958, 0.541196100, 0.275899379 }; i = 0; for (row = 0; row < DCTSIZE; row++) { for (col = 0; col < DCTSIZE; col++) { fmtbl[i] = (FLOAT_MULT_TYPE) ((double) qtbl->quantval[i] * aanscalefactor[row] * aanscalefactor[col]); i++; } } } break; #endif default: ERREXIT(cinfo, JERR_NOT_COMPILED); break; } } } /* * Initialize IDCT manager. */ GLOBAL(void) jinit_inverse_dct (j_decompress_ptr cinfo) { my_idct_ptr idct; int ci; jpeg_component_info *compptr; idct = (my_idct_ptr) (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_idct_controller)); cinfo->idct = (struct jpeg_inverse_dct *) idct; idct->pub.start_pass = start_pass; for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components; ci++, compptr++) { /* Allocate and pre-zero a multiplier table for each component */ compptr->dct_table = (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(multiplier_table)); MEMZERO(compptr->dct_table, SIZEOF(multiplier_table)); /* Mark multiplier table not yet set up for any method */ idct->cur_method[ci] = -1; } }