The Independent JPEG Group's JPEG software v6
diff --git a/jddctmgr.c b/jddctmgr.c
index 0dd7716..71215f1 100644
--- a/jddctmgr.c
+++ b/jddctmgr.c
@@ -1,14 +1,14 @@
/*
* jddctmgr.c
*
- * Copyright (C) 1994, Thomas G. Lane.
+ * Copyright (C) 1994-1995, 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 pass setup.
+ * 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
@@ -21,30 +21,50 @@
#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 */
- /* Record the IDCT method type actually selected for each component */
- J_DCT_METHOD real_method[MAX_COMPONENTS];
+ /* 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;
-/* ZIG[i] is the zigzag-order position of the i'th element of a DCT block */
-/* read in natural order (left to right, top to bottom). */
-static const int ZIG[DCTSIZE2] = {
- 0, 1, 5, 6, 14, 15, 27, 28,
- 2, 4, 7, 13, 16, 26, 29, 42,
- 3, 8, 12, 17, 25, 30, 41, 43,
- 9, 11, 18, 24, 31, 40, 44, 53,
- 10, 19, 23, 32, 39, 45, 52, 54,
- 20, 22, 33, 38, 46, 51, 55, 60,
- 21, 34, 37, 47, 50, 56, 59, 61,
- 35, 36, 48, 49, 57, 58, 62, 63
-};
+/* 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,
@@ -60,51 +80,92 @@
/*
- * Initialize for an input scan.
- *
- * Verify that all referenced Q-tables are present, and set up
- * the multiplier table for each one.
- * With a multiple-scan JPEG file, this is called during each input scan,
- * NOT during the final output pass where the IDCT is actually done.
- * The purpose is to save away the current Q-table contents just in case
- * the encoder changes tables between scans. This decoder will dequantize
- * any component using the Q-table which was current at the start of the
- * first scan using that component.
+ * Prepare for an output pass.
+ * Here we select the proper IDCT routine for each component and build
+ * a matching multiplier table.
*/
METHODDEF void
-start_input_pass (j_decompress_ptr cinfo)
+start_pass (j_decompress_ptr cinfo)
{
my_idct_ptr idct = (my_idct_ptr) cinfo->idct;
- int ci, qtblno, i;
+ int ci, i;
jpeg_component_info *compptr;
+ int method = 0;
+ inverse_DCT_method_ptr method_ptr = NULL;
JQUANT_TBL * qtbl;
- for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
- compptr = cinfo->cur_comp_info[ci];
- qtblno = compptr->quant_tbl_no;
- /* Make sure specified quantization table is present */
- if (qtblno < 0 || qtblno >= NUM_QUANT_TBLS ||
- cinfo->quant_tbl_ptrs[qtblno] == NULL)
- ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, qtblno);
- qtbl = cinfo->quant_tbl_ptrs[qtblno];
- /* Create multiplier table from quant table, unless we already did so. */
- if (compptr->dct_table != NULL)
+ 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;
- switch (idct->real_method[compptr->component_index]) {
+ 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 in natural order as ints.
*/
- ISLOW_MULT_TYPE * ismtbl;
- compptr->dct_table =
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- DCTSIZE2 * SIZEOF(ISLOW_MULT_TYPE));
- ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
+ ISLOW_MULT_TYPE * ismtbl = (ISLOW_MULT_TYPE *) compptr->dct_table;
for (i = 0; i < DCTSIZE2; i++) {
- ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[ZIG[i]];
+ ismtbl[i] = (ISLOW_MULT_TYPE) qtbl->quantval[jpeg_zigzag_order[i]];
}
}
break;
@@ -119,7 +180,7 @@
* For integer operation, the multiplier table is to be scaled by
* IFAST_SCALE_BITS. The multipliers are stored in natural order.
*/
- IFAST_MULT_TYPE * ifmtbl;
+ 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 */
@@ -134,13 +195,9 @@
};
SHIFT_TEMPS
- compptr->dct_table =
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- DCTSIZE2 * SIZEOF(IFAST_MULT_TYPE));
- ifmtbl = (IFAST_MULT_TYPE *) compptr->dct_table;
for (i = 0; i < DCTSIZE2; i++) {
ifmtbl[i] = (IFAST_MULT_TYPE)
- DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[ZIG[i]],
+ DESCALE(MULTIPLY16V16((INT32) qtbl->quantval[jpeg_zigzag_order[i]],
(INT32) aanscales[i]),
CONST_BITS-IFAST_SCALE_BITS);
}
@@ -156,22 +213,18 @@
* scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
* The multipliers are stored in natural order.
*/
- FLOAT_MULT_TYPE * fmtbl;
+ 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
};
- compptr->dct_table =
- (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
- DCTSIZE2 * SIZEOF(FLOAT_MULT_TYPE));
- fmtbl = (FLOAT_MULT_TYPE *) compptr->dct_table;
i = 0;
for (row = 0; row < DCTSIZE; row++) {
for (col = 0; col < DCTSIZE; col++) {
fmtbl[i] = (FLOAT_MULT_TYPE)
- ((double) qtbl->quantval[ZIG[i]] *
+ ((double) qtbl->quantval[jpeg_zigzag_order[i]] *
aanscalefactor[row] * aanscalefactor[col]);
i++;
}
@@ -188,32 +241,6 @@
/*
- * Prepare for an output pass that will actually perform IDCTs.
- *
- * start_input_pass should already have been done for all components
- * of interest; we need only verify that this is true.
- * Note that uninteresting components are not required to have loaded tables.
- * This allows the master controller to stop before reading the whole file
- * if it has obtained the data for the interesting component(s).
- */
-
-METHODDEF void
-start_output_pass (j_decompress_ptr cinfo)
-{
- jpeg_component_info *compptr;
- int ci;
-
- for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
- ci++, compptr++) {
- if (! compptr->component_needed)
- continue;
- if (compptr->dct_table == NULL)
- ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, compptr->quant_tbl_no);
- }
-}
-
-
-/*
* Initialize IDCT manager.
*/
@@ -228,55 +255,16 @@
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(my_idct_controller));
cinfo->idct = (struct jpeg_inverse_dct *) idct;
- idct->pub.start_input_pass = start_input_pass;
- idct->pub.start_output_pass = start_output_pass;
+ idct->pub.start_pass = start_pass;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
- compptr->dct_table = NULL; /* initialize tables to "not prepared" */
- switch (compptr->DCT_scaled_size) {
-#ifdef IDCT_SCALING_SUPPORTED
- case 1:
- idct->pub.inverse_DCT[ci] = jpeg_idct_1x1;
- idct->real_method[ci] = JDCT_ISLOW; /* jidctred uses islow-style table */
- break;
- case 2:
- idct->pub.inverse_DCT[ci] = jpeg_idct_2x2;
- idct->real_method[ci] = JDCT_ISLOW; /* jidctred uses islow-style table */
- break;
- case 4:
- idct->pub.inverse_DCT[ci] = jpeg_idct_4x4;
- idct->real_method[ci] = JDCT_ISLOW; /* jidctred uses islow-style table */
- break;
-#endif
- case DCTSIZE:
- switch (cinfo->dct_method) {
-#ifdef DCT_ISLOW_SUPPORTED
- case JDCT_ISLOW:
- idct->pub.inverse_DCT[ci] = jpeg_idct_islow;
- idct->real_method[ci] = JDCT_ISLOW;
- break;
-#endif
-#ifdef DCT_IFAST_SUPPORTED
- case JDCT_IFAST:
- idct->pub.inverse_DCT[ci] = jpeg_idct_ifast;
- idct->real_method[ci] = JDCT_IFAST;
- break;
-#endif
-#ifdef DCT_FLOAT_SUPPORTED
- case JDCT_FLOAT:
- idct->pub.inverse_DCT[ci] = jpeg_idct_float;
- idct->real_method[ci] = JDCT_FLOAT;
- break;
-#endif
- default:
- ERREXIT(cinfo, JERR_NOT_COMPILED);
- break;
- }
- break;
- default:
- ERREXIT1(cinfo, JERR_BAD_DCTSIZE, compptr->DCT_scaled_size);
- break;
- }
+ /* 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;
}
}