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/*
* jidctred.c
*
* This file was part of the Independent JPEG Group's software:
* Copyright (C) 1994-1998, Thomas G. Lane.
* libjpeg-turbo Modifications:
* Copyright (C) 2015, 2022, D. R. Commander.
* For conditions of distribution and use, see the accompanying README.ijg
* file.
*
* This file contains inverse-DCT routines that produce reduced-size output:
* either 4x4, 2x2, or 1x1 pixels from an 8x8 DCT block.
*
* The implementation is based on the Loeffler, Ligtenberg and Moschytz (LL&M)
* algorithm used in jidctint.c. We simply replace each 8-to-8 1-D IDCT step
* with an 8-to-4 step that produces the four averages of two adjacent outputs
* (or an 8-to-2 step producing two averages of four outputs, for 2x2 output).
* These steps were derived by computing the corresponding values at the end
* of the normal LL&M code, then simplifying as much as possible.
*
* 1x1 is trivial: just take the DC coefficient divided by 8.
*
* See jidctint.c for additional comments.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdct.h" /* Private declarations for DCT subsystem */
#ifdef IDCT_SCALING_SUPPORTED
/*
* This module is specialized to the case DCTSIZE = 8.
*/
#if DCTSIZE != 8
Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */
#endif
/* Scaling is the same as in jidctint.c. */
#if BITS_IN_JSAMPLE == 8
#define CONST_BITS 13
#define PASS1_BITS 2
#else
#define CONST_BITS 13
#define PASS1_BITS 1 /* lose a little precision to avoid overflow */
#endif
/* Some C compilers fail to reduce "FIX(constant)" at compile time, thus
* causing a lot of useless floating-point operations at run time.
* To get around this we use the following pre-calculated constants.
* If you change CONST_BITS you may want to add appropriate values.
* (With a reasonable C compiler, you can just rely on the FIX() macro...)
*/
#if CONST_BITS == 13
#define FIX_0_211164243 ((JLONG)1730) /* FIX(0.211164243) */
#define FIX_0_509795579 ((JLONG)4176) /* FIX(0.509795579) */
#define FIX_0_601344887 ((JLONG)4926) /* FIX(0.601344887) */
#define FIX_0_720959822 ((JLONG)5906) /* FIX(0.720959822) */
#define FIX_0_765366865 ((JLONG)6270) /* FIX(0.765366865) */
#define FIX_0_850430095 ((JLONG)6967) /* FIX(0.850430095) */
#define FIX_0_899976223 ((JLONG)7373) /* FIX(0.899976223) */
#define FIX_1_061594337 ((JLONG)8697) /* FIX(1.061594337) */
#define FIX_1_272758580 ((JLONG)10426) /* FIX(1.272758580) */
#define FIX_1_451774981 ((JLONG)11893) /* FIX(1.451774981) */
#define FIX_1_847759065 ((JLONG)15137) /* FIX(1.847759065) */
#define FIX_2_172734803 ((JLONG)17799) /* FIX(2.172734803) */
#define FIX_2_562915447 ((JLONG)20995) /* FIX(2.562915447) */
#define FIX_3_624509785 ((JLONG)29692) /* FIX(3.624509785) */
#else
#define FIX_0_211164243 FIX(0.211164243)
#define FIX_0_509795579 FIX(0.509795579)
#define FIX_0_601344887 FIX(0.601344887)
#define FIX_0_720959822 FIX(0.720959822)
#define FIX_0_765366865 FIX(0.765366865)
#define FIX_0_850430095 FIX(0.850430095)
#define FIX_0_899976223 FIX(0.899976223)
#define FIX_1_061594337 FIX(1.061594337)
#define FIX_1_272758580 FIX(1.272758580)
#define FIX_1_451774981 FIX(1.451774981)
#define FIX_1_847759065 FIX(1.847759065)
#define FIX_2_172734803 FIX(2.172734803)
#define FIX_2_562915447 FIX(2.562915447)
#define FIX_3_624509785 FIX(3.624509785)
#endif
/* Multiply a JLONG variable by a JLONG constant to yield a JLONG result.
* For 8-bit samples with the recommended scaling, all the variable
* and constant values involved are no more than 16 bits wide, so a
* 16x16->32 bit multiply can be used instead of a full 32x32 multiply.
* For 12-bit samples, a full 32-bit multiplication will be needed.
*/
#if BITS_IN_JSAMPLE == 8
#define MULTIPLY(var, const) MULTIPLY16C16(var, const)
#else
#define MULTIPLY(var, const) ((var) * (const))
#endif
/* Dequantize a coefficient by multiplying it by the multiplier-table
* entry; produce an int result. In this module, both inputs and result
* are 16 bits or less, so either int or short multiply will work.
*/
#define DEQUANTIZE(coef, quantval) (((ISLOW_MULT_TYPE)(coef)) * (quantval))
/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 4x4 output block.
*/
GLOBAL(void)
_jpeg_idct_4x4(j_decompress_ptr cinfo, jpeg_component_info *compptr,
JCOEFPTR coef_block, _JSAMPARRAY output_buf,
JDIMENSION output_col)
{
JLONG tmp0, tmp2, tmp10, tmp12;
JLONG z1, z2, z3, z4;
JCOEFPTR inptr;
ISLOW_MULT_TYPE *quantptr;
int *wsptr;
_JSAMPROW outptr;
_JSAMPLE *range_limit = IDCT_range_limit(cinfo);
int ctr;
int workspace[DCTSIZE * 4]; /* buffers data between passes */
SHIFT_TEMPS
/* Pass 1: process columns from input, store into work array. */
inptr = coef_block;
quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
wsptr = workspace;
for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
/* Don't bother to process column 4, because second pass won't use it */
if (ctr == DCTSIZE - 4)
continue;
if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 2] == 0 &&
inptr[DCTSIZE * 3] == 0 && inptr[DCTSIZE * 5] == 0 &&
inptr[DCTSIZE * 6] == 0 && inptr[DCTSIZE * 7] == 0) {
/* AC terms all zero; we need not examine term 4 for 4x4 output */
int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
quantptr[DCTSIZE * 0]), PASS1_BITS);
wsptr[DCTSIZE * 0] = dcval;
wsptr[DCTSIZE * 1] = dcval;
wsptr[DCTSIZE * 2] = dcval;
wsptr[DCTSIZE * 3] = dcval;
continue;
}
/* Even part */
tmp0 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
tmp0 = LEFT_SHIFT(tmp0, CONST_BITS + 1);
z2 = DEQUANTIZE(inptr[DCTSIZE * 2], quantptr[DCTSIZE * 2]);
z3 = DEQUANTIZE(inptr[DCTSIZE * 6], quantptr[DCTSIZE * 6]);
tmp2 = MULTIPLY(z2, FIX_1_847759065) + MULTIPLY(z3, -FIX_0_765366865);
tmp10 = tmp0 + tmp2;
tmp12 = tmp0 - tmp2;
/* Odd part */
z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
z2 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
z3 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
z4 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);
tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */
MULTIPLY(z2, FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */
MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */
MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * ( c5+c7) */
tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */
MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */
MULTIPLY(z3, FIX_0_899976223) + /* sqrt(2) * (c3-c7) */
MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
/* Final output stage */
wsptr[DCTSIZE * 0] =
(int)DESCALE(tmp10 + tmp2, CONST_BITS - PASS1_BITS + 1);
wsptr[DCTSIZE * 3] =
(int)DESCALE(tmp10 - tmp2, CONST_BITS - PASS1_BITS + 1);
wsptr[DCTSIZE * 1] =
(int)DESCALE(tmp12 + tmp0, CONST_BITS - PASS1_BITS + 1);
wsptr[DCTSIZE * 2] =
(int)DESCALE(tmp12 - tmp0, CONST_BITS - PASS1_BITS + 1);
}
/* Pass 2: process 4 rows from work array, store into output array. */
wsptr = workspace;
for (ctr = 0; ctr < 4; ctr++) {
outptr = output_buf[ctr] + output_col;
/* It's not clear whether a zero row test is worthwhile here ... */
#ifndef NO_ZERO_ROW_TEST
if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 &&
wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
/* AC terms all zero */
_JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
PASS1_BITS + 3) & RANGE_MASK];
outptr[0] = dcval;
outptr[1] = dcval;
outptr[2] = dcval;
outptr[3] = dcval;
wsptr += DCTSIZE; /* advance pointer to next row */
continue;
}
#endif
/* Even part */
tmp0 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 1);
tmp2 = MULTIPLY((JLONG)wsptr[2], FIX_1_847759065) +
MULTIPLY((JLONG)wsptr[6], -FIX_0_765366865);
tmp10 = tmp0 + tmp2;
tmp12 = tmp0 - tmp2;
/* Odd part */
z1 = (JLONG)wsptr[7];
z2 = (JLONG)wsptr[5];
z3 = (JLONG)wsptr[3];
z4 = (JLONG)wsptr[1];
tmp0 = MULTIPLY(z1, -FIX_0_211164243) + /* sqrt(2) * ( c3-c1) */
MULTIPLY(z2, FIX_1_451774981) + /* sqrt(2) * ( c3+c7) */
MULTIPLY(z3, -FIX_2_172734803) + /* sqrt(2) * (-c1-c5) */
MULTIPLY(z4, FIX_1_061594337); /* sqrt(2) * ( c5+c7) */
tmp2 = MULTIPLY(z1, -FIX_0_509795579) + /* sqrt(2) * (c7-c5) */
MULTIPLY(z2, -FIX_0_601344887) + /* sqrt(2) * (c5-c1) */
MULTIPLY(z3, FIX_0_899976223) + /* sqrt(2) * (c3-c7) */
MULTIPLY(z4, FIX_2_562915447); /* sqrt(2) * (c1+c3) */
/* Final output stage */
outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp2,
CONST_BITS + PASS1_BITS + 3 + 1) &
RANGE_MASK];
outptr[3] = range_limit[(int)DESCALE(tmp10 - tmp2,
CONST_BITS + PASS1_BITS + 3 + 1) &
RANGE_MASK];
outptr[1] = range_limit[(int)DESCALE(tmp12 + tmp0,
CONST_BITS + PASS1_BITS + 3 + 1) &
RANGE_MASK];
outptr[2] = range_limit[(int)DESCALE(tmp12 - tmp0,
CONST_BITS + PASS1_BITS + 3 + 1) &
RANGE_MASK];
wsptr += DCTSIZE; /* advance pointer to next row */
}
}
/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 2x2 output block.
*/
GLOBAL(void)
_jpeg_idct_2x2(j_decompress_ptr cinfo, jpeg_component_info *compptr,
JCOEFPTR coef_block, _JSAMPARRAY output_buf,
JDIMENSION output_col)
{
JLONG tmp0, tmp10, z1;
JCOEFPTR inptr;
ISLOW_MULT_TYPE *quantptr;
int *wsptr;
_JSAMPROW outptr;
_JSAMPLE *range_limit = IDCT_range_limit(cinfo);
int ctr;
int workspace[DCTSIZE * 2]; /* buffers data between passes */
SHIFT_TEMPS
/* Pass 1: process columns from input, store into work array. */
inptr = coef_block;
quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
wsptr = workspace;
for (ctr = DCTSIZE; ctr > 0; inptr++, quantptr++, wsptr++, ctr--) {
/* Don't bother to process columns 2,4,6 */
if (ctr == DCTSIZE - 2 || ctr == DCTSIZE - 4 || ctr == DCTSIZE - 6)
continue;
if (inptr[DCTSIZE * 1] == 0 && inptr[DCTSIZE * 3] == 0 &&
inptr[DCTSIZE * 5] == 0 && inptr[DCTSIZE * 7] == 0) {
/* AC terms all zero; we need not examine terms 2,4,6 for 2x2 output */
int dcval = LEFT_SHIFT(DEQUANTIZE(inptr[DCTSIZE * 0],
quantptr[DCTSIZE * 0]), PASS1_BITS);
wsptr[DCTSIZE * 0] = dcval;
wsptr[DCTSIZE * 1] = dcval;
continue;
}
/* Even part */
z1 = DEQUANTIZE(inptr[DCTSIZE * 0], quantptr[DCTSIZE * 0]);
tmp10 = LEFT_SHIFT(z1, CONST_BITS + 2);
/* Odd part */
z1 = DEQUANTIZE(inptr[DCTSIZE * 7], quantptr[DCTSIZE * 7]);
tmp0 = MULTIPLY(z1, -FIX_0_720959822); /* sqrt(2) * ( c7-c5+c3-c1) */
z1 = DEQUANTIZE(inptr[DCTSIZE * 5], quantptr[DCTSIZE * 5]);
tmp0 += MULTIPLY(z1, FIX_0_850430095); /* sqrt(2) * (-c1+c3+c5+c7) */
z1 = DEQUANTIZE(inptr[DCTSIZE * 3], quantptr[DCTSIZE * 3]);
tmp0 += MULTIPLY(z1, -FIX_1_272758580); /* sqrt(2) * (-c1+c3-c5-c7) */
z1 = DEQUANTIZE(inptr[DCTSIZE * 1], quantptr[DCTSIZE * 1]);
tmp0 += MULTIPLY(z1, FIX_3_624509785); /* sqrt(2) * ( c1+c3+c5+c7) */
/* Final output stage */
wsptr[DCTSIZE * 0] =
(int)DESCALE(tmp10 + tmp0, CONST_BITS - PASS1_BITS + 2);
wsptr[DCTSIZE * 1] =
(int)DESCALE(tmp10 - tmp0, CONST_BITS - PASS1_BITS + 2);
}
/* Pass 2: process 2 rows from work array, store into output array. */
wsptr = workspace;
for (ctr = 0; ctr < 2; ctr++) {
outptr = output_buf[ctr] + output_col;
/* It's not clear whether a zero row test is worthwhile here ... */
#ifndef NO_ZERO_ROW_TEST
if (wsptr[1] == 0 && wsptr[3] == 0 && wsptr[5] == 0 && wsptr[7] == 0) {
/* AC terms all zero */
_JSAMPLE dcval = range_limit[(int)DESCALE((JLONG)wsptr[0],
PASS1_BITS + 3) & RANGE_MASK];
outptr[0] = dcval;
outptr[1] = dcval;
wsptr += DCTSIZE; /* advance pointer to next row */
continue;
}
#endif
/* Even part */
tmp10 = LEFT_SHIFT((JLONG)wsptr[0], CONST_BITS + 2);
/* Odd part */
tmp0 = MULTIPLY((JLONG)wsptr[7], -FIX_0_720959822) + /* sqrt(2) * ( c7-c5+c3-c1) */
MULTIPLY((JLONG)wsptr[5], FIX_0_850430095) + /* sqrt(2) * (-c1+c3+c5+c7) */
MULTIPLY((JLONG)wsptr[3], -FIX_1_272758580) + /* sqrt(2) * (-c1+c3-c5-c7) */
MULTIPLY((JLONG)wsptr[1], FIX_3_624509785); /* sqrt(2) * ( c1+c3+c5+c7) */
/* Final output stage */
outptr[0] = range_limit[(int)DESCALE(tmp10 + tmp0,
CONST_BITS + PASS1_BITS + 3 + 2) &
RANGE_MASK];
outptr[1] = range_limit[(int)DESCALE(tmp10 - tmp0,
CONST_BITS + PASS1_BITS + 3 + 2) &
RANGE_MASK];
wsptr += DCTSIZE; /* advance pointer to next row */
}
}
/*
* Perform dequantization and inverse DCT on one block of coefficients,
* producing a reduced-size 1x1 output block.
*/
GLOBAL(void)
_jpeg_idct_1x1(j_decompress_ptr cinfo, jpeg_component_info *compptr,
JCOEFPTR coef_block, _JSAMPARRAY output_buf,
JDIMENSION output_col)
{
int dcval;
ISLOW_MULT_TYPE *quantptr;
_JSAMPLE *range_limit = IDCT_range_limit(cinfo);
SHIFT_TEMPS
/* We hardly need an inverse DCT routine for this: just take the
* average pixel value, which is one-eighth of the DC coefficient.
*/
quantptr = (ISLOW_MULT_TYPE *)compptr->dct_table;
dcval = DEQUANTIZE(coef_block[0], quantptr[0]);
dcval = (int)DESCALE((JLONG)dcval, 3);
output_buf[0][output_col] = range_limit[dcval & RANGE_MASK];
}
#endif /* IDCT_SCALING_SUPPORTED */