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f5f8f5aadc82e6d4c13187311626342f722ba6e4
mozjpeg/jidctred.c
DRC e8b40f3c2b Vastly improve 12-bit JPEG integration 
The Gordian knot that 7fec5074f9 attempted
to unravel was caused by the fact that there are several
data-precision-dependent (JSAMPLE-dependent) fields and methods in the
exposed libjpeg API structures, and if you change the exposed libjpeg
API structures, then you have to change the whole API.  If you change
the whole API, then you have to provide a whole new library to support
the new API, and that makes it difficult to support multiple data
precisions in the same application.  (It is not impossible, as example.c
demonstrated, but using data-precision-dependent libjpeg API structures
would have made the cjpeg, djpeg, and jpegtran source code hard to read,
so it made more sense to build, install, and package 12-bit-specific
versions of those applications.)

Unfortunately, the result of that initial integration effort was an
unreadable and unmaintainable mess, which is a problem for a library
that is an ISO/ITU-T reference implementation.  Also, as I dug into the
problem of lossless JPEG support, I realized that 16-bit lossless JPEG
images are a thing, and supporting yet another version of the libjpeg
API just for those images is untenable.

In fact, however, the touch points for JSAMPLE in the exposed libjpeg
API structures are minimal:

  - The colormap and sample_range_limit fields in jpeg_decompress_struct
  - The alloc_sarray() and access_virt_sarray() methods in
    jpeg_memory_mgr
  - jpeg_write_scanlines() and jpeg_write_raw_data()
  - jpeg_read_scanlines() and jpeg_read_raw_data()
  - jpeg_skip_scanlines() and jpeg_crop_scanline()
    (This is subtle, but both of those functions use JSAMPLE-dependent
    opaque structures behind the scenes.)

It is much more readable and maintainable to provide 12-bit-specific
versions of those six top-level API functions and to document that the
aforementioned methods and fields must be type-cast when using 12-bit
samples.  Since that eliminates the need to provide a 12-bit-specific
version of the exposed libjpeg API structures, we can:

  - Compile only the precision-dependent libjpeg modules (the
    coefficient buffer controllers, the colorspace converters, the
    DCT/IDCT managers, the main buffer controllers, the preprocessing
    and postprocessing controller, the downsampler and upsamplers, the
    quantizers, the integer DCT methods, and the IDCT methods) for
    multiple data precisions.
  - Introduce 12-bit-specific methods into the various internal
    structures defined in jpegint.h.
  - Create precision-independent data type, macro, method, field, and
    function names that are prefixed by an underscore, and use an
    internal header to convert those into precision-dependent data
    type, macro, method, field, and function names, based on the value
    of BITS_IN_JSAMPLE, when compiling the precision-dependent libjpeg
    modules.
  - Expose precision-dependent jinit*() functions for each of the
    precision-dependent libjpeg modules.
  - Abstract the precision-dependent libjpeg modules by calling the
    appropriate precision-dependent jinit*() function, based on the
    value of cinfo->data_precision, from top-level libjpeg API
    functions.
2022-11-04 12:30:33 -05:00

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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 */
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