287 lines
10 KiB
C
287 lines
10 KiB
C
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/*
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* jidctflt.c
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*
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* Copyright (C) 1994-1998, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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*
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* The authors make NO WARRANTY or representation, either express or implied,
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* with respect to this software, its quality, accuracy, merchantability, or
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* fitness for a particular purpose. This software is provided "AS IS", and you,
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* its user, assume the entire risk as to its quality and accuracy.
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*
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* This software is copyright (C) 1991-1998, Thomas G. Lane.
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* All Rights Reserved except as specified below.
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*
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* Permission is hereby granted to use, copy, modify, and distribute this
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* software (or portions thereof) for any purpose, without fee, subject to these
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* conditions:
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* (1) If any part of the source code for this software is distributed, then this
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* README file must be included, with this copyright and no-warranty notice
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* unaltered; and any additions, deletions, or changes to the original files
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* must be clearly indicated in accompanying documentation.
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* (2) If only executable code is distributed, then the accompanying
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* documentation must state that "this software is based in part on the work of
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* the Independent JPEG Group".
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* (3) Permission for use of this software is granted only if the user accepts
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* full responsibility for any undesirable consequences; the authors accept
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* NO LIABILITY for damages of any kind.
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*
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* These conditions apply to any software derived from or based on the IJG code,
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* not just to the unmodified library. If you use our work, you ought to
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* acknowledge us.
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*
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* Permission is NOT granted for the use of any IJG author's name or company name
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* in advertising or publicity relating to this software or products derived from
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* it. This software may be referred to only as "the Independent JPEG Group's
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* software".
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*
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* We specifically permit and encourage the use of this software as the basis of
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* commercial products, provided that all warranty or liability claims are
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* assumed by the product vendor.
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*
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*
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* This file contains a floating-point implementation of the
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* inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
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* must also perform dequantization of the input coefficients.
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*
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* This implementation should be more accurate than either of the integer
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* IDCT implementations. However, it may not give the same results on all
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* machines because of differences in roundoff behavior. Speed will depend
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* on the hardware's floating point capacity.
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*
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* A 2-D IDCT can be done by 1-D IDCT on each column followed by 1-D IDCT
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* on each row (or vice versa, but it's more convenient to emit a row at
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* a time). Direct algorithms are also available, but they are much more
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* complex and seem not to be any faster when reduced to code.
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*
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* This implementation is based on Arai, Agui, and Nakajima's algorithm for
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* scaled DCT. Their original paper (Trans. IEICE E-71(11):1095) is in
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* Japanese, but the algorithm is described in the Pennebaker & Mitchell
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* JPEG textbook (see REFERENCES section in file README). The following code
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* is based directly on figure 4-8 in P&M.
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* While an 8-point DCT cannot be done in less than 11 multiplies, it is
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* possible to arrange the computation so that many of the multiplies are
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* simple scalings of the final outputs. These multiplies can then be
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* folded into the multiplications or divisions by the JPEG quantization
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* table entries. The AA&N method leaves only 5 multiplies and 29 adds
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* to be done in the DCT itself.
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* The primary disadvantage of this method is that with a fixed-point
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* implementation, accuracy is lost due to imprecise representation of the
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* scaled quantization values. However, that problem does not arise if
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* we use floating point arithmetic.
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*/
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#include "tinyjpeg-internal.h"
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#define FAST_FLOAT float
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#define DCTSIZE 8
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#define DCTSIZE2 (DCTSIZE*DCTSIZE)
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#define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
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#if 0 && defined(__GNUC__) && (defined(__i686__))
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// || defined(__x86_64__))
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static inline unsigned char descale_and_clamp(int x, int shift)
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{
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__asm__ (
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"add %3,%1\n"
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"\tsar %2,%1\n"
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"\tsub $-128,%1\n"
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"\tcmovl %5,%1\n" /* Use the sub to compare to 0 */
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"\tcmpl %4,%1\n"
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"\tcmovg %4,%1\n"
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: "=r"(x)
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: "0"(x), "Ir"(shift), "ir"(1UL<<(shift-1)), "r" (0xff), "r" (0)
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);
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return x;
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}
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#else
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static __inline unsigned char descale_and_clamp(int x, int shift)
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{
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x += (1UL<<(shift-1));
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if (x<0)
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x = (x >> shift) | ((~(0UL)) << (32-(shift)));
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else
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x >>= shift;
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x += 128;
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if (x>255)
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return 255;
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else if (x<0)
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return 0;
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else
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return x;
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}
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#endif
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/*
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* Perform dequantization and inverse DCT on one block of coefficients.
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*/
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void
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tinyjpeg_idct_float (struct component *compptr, uint8_t *output_buf, int stride)
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{
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FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
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FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
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FAST_FLOAT z5, z10, z11, z12, z13;
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int16_t *inptr;
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FAST_FLOAT *quantptr;
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FAST_FLOAT *wsptr;
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uint8_t *outptr;
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int ctr;
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FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
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/* Pass 1: process columns from input, store into work array. */
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inptr = compptr->DCT;
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quantptr = compptr->Q_table;
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wsptr = workspace;
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for (ctr = DCTSIZE; ctr > 0; ctr--) {
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/* Due to quantization, we will usually find that many of the input
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* coefficients are zero, especially the AC terms. We can exploit this
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* by short-circuiting the IDCT calculation for any column in which all
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* the AC terms are zero. In that case each output is equal to the
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* DC coefficient (with scale factor as needed).
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* With typical images and quantization tables, half or more of the
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* column DCT calculations can be simplified this way.
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*/
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if (inptr[DCTSIZE*1] == 0 && inptr[DCTSIZE*2] == 0 &&
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inptr[DCTSIZE*3] == 0 && inptr[DCTSIZE*4] == 0 &&
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inptr[DCTSIZE*5] == 0 && inptr[DCTSIZE*6] == 0 &&
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inptr[DCTSIZE*7] == 0) {
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/* AC terms all zero */
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FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
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wsptr[DCTSIZE*0] = dcval;
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wsptr[DCTSIZE*1] = dcval;
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wsptr[DCTSIZE*2] = dcval;
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wsptr[DCTSIZE*3] = dcval;
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wsptr[DCTSIZE*4] = dcval;
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wsptr[DCTSIZE*5] = dcval;
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wsptr[DCTSIZE*6] = dcval;
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wsptr[DCTSIZE*7] = dcval;
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inptr++; /* advance pointers to next column */
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quantptr++;
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wsptr++;
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continue;
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}
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/* Even part */
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tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
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tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
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tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
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tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
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tmp10 = tmp0 + tmp2; /* phase 3 */
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tmp11 = tmp0 - tmp2;
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tmp13 = tmp1 + tmp3; /* phases 5-3 */
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tmp12 = (tmp1 - tmp3) * ((FAST_FLOAT) 1.414213562) - tmp13; /* 2*c4 */
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tmp0 = tmp10 + tmp13; /* phase 2 */
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tmp3 = tmp10 - tmp13;
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tmp1 = tmp11 + tmp12;
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tmp2 = tmp11 - tmp12;
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/* Odd part */
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tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
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tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
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tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
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tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
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z13 = tmp6 + tmp5; /* phase 6 */
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z10 = tmp6 - tmp5;
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z11 = tmp4 + tmp7;
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z12 = tmp4 - tmp7;
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tmp7 = z11 + z13; /* phase 5 */
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tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562); /* 2*c4 */
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z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
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tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
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tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
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tmp6 = tmp12 - tmp7; /* phase 2 */
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tmp5 = tmp11 - tmp6;
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tmp4 = tmp10 + tmp5;
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wsptr[DCTSIZE*0] = tmp0 + tmp7;
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wsptr[DCTSIZE*7] = tmp0 - tmp7;
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wsptr[DCTSIZE*1] = tmp1 + tmp6;
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wsptr[DCTSIZE*6] = tmp1 - tmp6;
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wsptr[DCTSIZE*2] = tmp2 + tmp5;
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wsptr[DCTSIZE*5] = tmp2 - tmp5;
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wsptr[DCTSIZE*4] = tmp3 + tmp4;
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wsptr[DCTSIZE*3] = tmp3 - tmp4;
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inptr++; /* advance pointers to next column */
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quantptr++;
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wsptr++;
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}
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/* Pass 2: process rows from work array, store into output array. */
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/* Note that we must descale the results by a factor of 8 == 2**3. */
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wsptr = workspace;
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outptr = output_buf;
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for (ctr = 0; ctr < DCTSIZE; ctr++) {
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/* Rows of zeroes can be exploited in the same way as we did with columns.
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* However, the column calculation has created many nonzero AC terms, so
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* the simplification applies less often (typically 5% to 10% of the time).
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* And testing floats for zero is relatively expensive, so we don't bother.
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*/
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/* Even part */
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tmp10 = wsptr[0] + wsptr[4];
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tmp11 = wsptr[0] - wsptr[4];
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tmp13 = wsptr[2] + wsptr[6];
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tmp12 = (wsptr[2] - wsptr[6]) * ((FAST_FLOAT) 1.414213562) - tmp13;
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tmp0 = tmp10 + tmp13;
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tmp3 = tmp10 - tmp13;
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tmp1 = tmp11 + tmp12;
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tmp2 = tmp11 - tmp12;
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/* Odd part */
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z13 = wsptr[5] + wsptr[3];
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z10 = wsptr[5] - wsptr[3];
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z11 = wsptr[1] + wsptr[7];
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z12 = wsptr[1] - wsptr[7];
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tmp7 = z11 + z13;
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tmp11 = (z11 - z13) * ((FAST_FLOAT) 1.414213562);
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z5 = (z10 + z12) * ((FAST_FLOAT) 1.847759065); /* 2*c2 */
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tmp10 = ((FAST_FLOAT) 1.082392200) * z12 - z5; /* 2*(c2-c6) */
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tmp12 = ((FAST_FLOAT) -2.613125930) * z10 + z5; /* -2*(c2+c6) */
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tmp6 = tmp12 - tmp7;
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tmp5 = tmp11 - tmp6;
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tmp4 = tmp10 + tmp5;
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/* Final output stage: scale down by a factor of 8 and range-limit */
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outptr[0] = descale_and_clamp((int)(tmp0 + tmp7), 3);
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outptr[7] = descale_and_clamp((int)(tmp0 - tmp7), 3);
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outptr[1] = descale_and_clamp((int)(tmp1 + tmp6), 3);
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outptr[6] = descale_and_clamp((int)(tmp1 - tmp6), 3);
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outptr[2] = descale_and_clamp((int)(tmp2 + tmp5), 3);
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outptr[5] = descale_and_clamp((int)(tmp2 - tmp5), 3);
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outptr[4] = descale_and_clamp((int)(tmp3 + tmp4), 3);
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outptr[3] = descale_and_clamp((int)(tmp3 - tmp4), 3);
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wsptr += DCTSIZE; /* advance pointer to next row */
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outptr += stride;
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}
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}
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