/*+ −
* 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;+ −
}+ −
}+ −