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/* |
* 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. |
*/ |
|
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/* Private subobject for this module */ |
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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; |
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typedef my_idct_controller * my_idct_ptr; |
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/* Allocated multiplier tables: big enough for any supported variant */ |
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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; |
} |
} |