mirror of
https://github.com/aseprite/aseprite.git
synced 2024-12-29 09:23:32 +00:00
243 lines
8.5 KiB
C
243 lines
8.5 KiB
C
/*
|
|
* jidctflt.c
|
|
*
|
|
* Copyright (C) 1994-1998, 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 a floating-point implementation of the
|
|
* inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
|
|
* must also perform dequantization of the input coefficients.
|
|
*
|
|
* This implementation should be more accurate than either of the integer
|
|
* IDCT implementations. However, it may not give the same results on all
|
|
* machines because of differences in roundoff behavior. Speed will depend
|
|
* on the hardware's floating point capacity.
|
|
*
|
|
* A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
|
|
* on each row (or vice versa, but it's more convenient to emit a row at
|
|
* a time). Direct algorithms are also available, but they are much more
|
|
* complex and seem not to be any faster when reduced to code.
|
|
*
|
|
* This implementation is based on Arai, Agui, and Nakajima's algorithm for
|
|
* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
|
|
* Japanese, but the algorithm is described in the Pennebaker & Mitchell
|
|
* JPEG textbook (see REFERENCES section in file README). The following code
|
|
* is based directly on figure 4-8 in P&M.
|
|
* While an 8-point DCT cannot be done in less than 11 multiplies, it is
|
|
* possible to arrange the computation so that many of the multiplies are
|
|
* simple scalings of the final outputs. These multiplies can then be
|
|
* folded into the multiplications or divisions by the JPEG quantization
|
|
* table entries. The AA&N method leaves only 5 multiplies and 29 adds
|
|
* to be done in the DCT itself.
|
|
* The primary disadvantage of this method is that with a fixed-point
|
|
* implementation, accuracy is lost due to imprecise representation of the
|
|
* scaled quantization values. However, that problem does not arise if
|
|
* we use floating point arithmetic.
|
|
*/
|
|
|
|
#define JPEG_INTERNALS
|
|
#include "jinclude.h"
|
|
#include "jpeglib.h"
|
|
#include "jdct.h" /* Private declarations for DCT subsystem */
|
|
|
|
#ifdef DCT_FLOAT_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
|
|
|
|
|
|
/* Dequantize a coefficient by multiplying it by the multiplier-table
|
|
* entry; produce a float result.
|
|
*/
|
|
|
|
#define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
|
|
|
|
|
|
/*
|
|
* Perform dequantization and inverse DCT on one block of coefficients.
|
|
*/
|
|
|
|
GLOBAL(void)
|
|
jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
|
|
JCOEFPTR coef_block,
|
|
JSAMPARRAY output_buf, JDIMENSION output_col)
|
|
{
|
|
FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
|
|
FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
|
|
FAST_FLOAT z5, z10, z11, z12, z13;
|
|
JCOEFPTR inptr;
|
|
FLOAT_MULT_TYPE * quantptr;
|
|
FAST_FLOAT * wsptr;
|
|
JSAMPROW outptr;
|
|
JSAMPLE *range_limit = IDCT_range_limit(cinfo);
|
|
int ctr;
|
|
FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
|
|
SHIFT_TEMPS
|
|
|
|
/* Pass 1: process columns from input, store into work array. */
|
|
|
|
inptr = coef_block;
|
|
quantptr = (FLOAT_MULT_TYPE *) compptr->dct_table;
|
|
wsptr = workspace;
|
|
for (ctr = DCTSIZE; ctr > 0; ctr--) {
|
|
/* Due to quantization, we will usually find that many of the input
|
|
* coefficients are zero, especially the AC terms. We can exploit this
|
|
* by short-circuiting the IDCT calculation for any column in which all
|
|
* the AC terms are zero. In that case each output is equal to the
|
|
* DC coefficient (with scale factor as needed).
|
|
* With typical images and quantization tables, half or more of the
|
|
* column DCT calculations can be simplified this way.
|
|
*/
|
|
|
|
if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
|
|
inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
|
|
inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
|
|
inptr[DCTSIZE*7] == 0) {
|
|
/* AC terms all zero */
|
|
FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
|
|
|
|
wsptr[DCTSIZE*0] = dcval;
|
|
wsptr[DCTSIZE*1] = dcval;
|
|
wsptr[DCTSIZE*2] = dcval;
|
|
wsptr[DCTSIZE*3] = dcval;
|
|
wsptr[DCTSIZE*4] = dcval;
|
|
wsptr[DCTSIZE*5] = dcval;
|
|
wsptr[DCTSIZE*6] = dcval;
|
|
wsptr[DCTSIZE*7] = dcval;
|
|
|
|
inptr++; /* advance pointers to next column */
|
|
quantptr++;
|
|
wsptr++;
|
|
continue;
|
|
}
|
|
|
|
/* Even part */
|
|
|
|
tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
|
|
tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
|
|
tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
|
|
tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
|
|
|
|
tmp10 = tmp0 + tmp2; /* phase 3 */
|
|
tmp11 = tmp0 - tmp2;
|
|
|
|
tmp13 = tmp1 + tmp3; /* phases 5-3 */
|
|
tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
|
|
|
|
tmp0 = tmp10 + tmp13; /* phase 2 */
|
|
tmp3 = tmp10 - tmp13;
|
|
tmp1 = tmp11 + tmp12;
|
|
tmp2 = tmp11 - tmp12;
|
|
|
|
/* Odd part */
|
|
|
|
tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
|
|
tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
|
|
tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
|
|
tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
|
|
|
|
z13 = tmp6 + tmp5; /* phase 6 */
|
|
z10 = tmp6 - tmp5;
|
|
z11 = tmp4 + tmp7;
|
|
z12 = tmp4 - tmp7;
|
|
|
|
tmp7 = z11 + z13; /* phase 5 */
|
|
tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
|
|
|
|
z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
|
|
tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
|
|
tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
|
|
|
|
tmp6 = tmp12 - tmp7; /* phase 2 */
|
|
tmp5 = tmp11 - tmp6;
|
|
tmp4 = tmp10 + tmp5;
|
|
|
|
wsptr[DCTSIZE*0] = tmp0 + tmp7;
|
|
wsptr[DCTSIZE*7] = tmp0 - tmp7;
|
|
wsptr[DCTSIZE*1] = tmp1 + tmp6;
|
|
wsptr[DCTSIZE*6] = tmp1 - tmp6;
|
|
wsptr[DCTSIZE*2] = tmp2 + tmp5;
|
|
wsptr[DCTSIZE*5] = tmp2 - tmp5;
|
|
wsptr[DCTSIZE*4] = tmp3 + tmp4;
|
|
wsptr[DCTSIZE*3] = tmp3 - tmp4;
|
|
|
|
inptr++; /* advance pointers to next column */
|
|
quantptr++;
|
|
wsptr++;
|
|
}
|
|
|
|
/* Pass 2: process rows from work array, store into output array. */
|
|
/* Note that we must descale the results by a factor of 8 == 2**3. */
|
|
|
|
wsptr = workspace;
|
|
for (ctr = 0; ctr < DCTSIZE; ctr++) {
|
|
outptr = output_buf[ctr] + output_col;
|
|
/* Rows of zeroes can be exploited in the same way as we did with columns.
|
|
* However, the column calculation has created many nonzero AC terms, so
|
|
* the simplification applies less often (typically 5% to 10% of the time).
|
|
* And testing floats for zero is relatively expensive, so we don't bother.
|
|
*/
|
|
|
|
/* Even part */
|
|
|
|
tmp10 = wsptr[0] + wsptr[4];
|
|
tmp11 = wsptr[0] - wsptr[4];
|
|
|
|
tmp13 = wsptr[2] + wsptr[6];
|
|
tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
|
|
|
|
tmp0 = tmp10 + tmp13;
|
|
tmp3 = tmp10 - tmp13;
|
|
tmp1 = tmp11 + tmp12;
|
|
tmp2 = tmp11 - tmp12;
|
|
|
|
/* Odd part */
|
|
|
|
z13 = wsptr[5] + wsptr[3];
|
|
z10 = wsptr[5] - wsptr[3];
|
|
z11 = wsptr[1] + wsptr[7];
|
|
z12 = wsptr[1] - wsptr[7];
|
|
|
|
tmp7 = z11 + z13;
|
|
tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
|
|
|
|
z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
|
|
tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
|
|
tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
|
|
|
|
tmp6 = tmp12 - tmp7;
|
|
tmp5 = tmp11 - tmp6;
|
|
tmp4 = tmp10 + tmp5;
|
|
|
|
/* Final output stage: scale down by a factor of 8 and range-limit */
|
|
|
|
outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
|
|
& RANGE_MASK];
|
|
outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
|
|
& RANGE_MASK];
|
|
outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
|
|
& RANGE_MASK];
|
|
outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
|
|
& RANGE_MASK];
|
|
outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
|
|
& RANGE_MASK];
|
|
outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
|
|
& RANGE_MASK];
|
|
outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
|
|
& RANGE_MASK];
|
|
outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
|
|
& RANGE_MASK];
|
|
|
|
wsptr += DCTSIZE; /* advance pointer to next row */
|
|
}
|
|
}
|
|
|
|
#endif /* DCT_FLOAT_SUPPORTED */
|