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-/*
- * jidctflt.c
- *
- * Copyright (C) 1994-1998, Thomas G. Lane.
- * This file is part of the Independent JPEG Group's software.
- *
- * The authors make NO WARRANTY or representation, either express or implied,
- * with respect to this software, its quality, accuracy, merchantability, or
- * fitness for a particular purpose. This software is provided "AS IS", and you,
- * its user, assume the entire risk as to its quality and accuracy.
- *
- * This software is copyright (C) 1991-1998, Thomas G. Lane.
- * All Rights Reserved except as specified below.
- *
- * Permission is hereby granted to use, copy, modify, and distribute this
- * software (or portions thereof) for any purpose, without fee, subject to these
- * conditions:
- * (1) If any part of the source code for this software is distributed, then this
- * README file must be included, with this copyright and no-warranty notice
- * unaltered; and any additions, deletions, or changes to the original files
- * must be clearly indicated in accompanying documentation.
- * (2) If only executable code is distributed, then the accompanying
- * documentation must state that "this software is based in part on the work of
- * the Independent JPEG Group".
- * (3) Permission for use of this software is granted only if the user accepts
- * full responsibility for any undesirable consequences; the authors accept
- * NO LIABILITY for damages of any kind.
- *
- * These conditions apply to any software derived from or based on the IJG code,
- * not just to the unmodified library. If you use our work, you ought to
- * acknowledge us.
- *
- * Permission is NOT granted for the use of any IJG author's name or company name
- * in advertising or publicity relating to this software or products derived from
- * it. This software may be referred to only as "the Independent JPEG Group's
- * software".
- *
- * We specifically permit and encourage the use of this software as the basis of
- * commercial products, provided that all warranty or liability claims are
- * assumed by the product vendor.
- *
- *
- * 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.
- */
-
-#include "tinyjpeg-internal.h"
-
-#define FAST_FLOAT float
-#define DCTSIZE 8
-#define DCTSIZE2 (DCTSIZE*DCTSIZE)
-
-#define DEQUANTIZE(coef,quantval) (((FAST_FLOAT) (coef)) * (quantval))
-
-#if 0 && defined(__GNUC__) && (defined(__i686__))
-// || defined(__x86_64__))
-
-static inline unsigned char descale_and_clamp(int x, int shift)
-{
- __asm__ (
- "add %3,%1\n"
- "\tsar %2,%1\n"
- "\tsub $-128,%1\n"
- "\tcmovl %5,%1\n" /* Use the sub to compare to 0 */
- "\tcmpl %4,%1\n"
- "\tcmovg %4,%1\n"
- : "=r"(x)
- : "0"(x), "Ir"(shift), "ir"(1UL<<(shift-1)), "r" (0xff), "r" (0)
- );
- return x;
-}
-
-#else
-static __inline unsigned char descale_and_clamp(int x, int shift)
-{
- x += (1UL<<(shift-1));
- if (x<0)
- x = (x >> shift) | ((~(0UL)) << (32-(shift)));
- else
- x >>= shift;
- x += 128;
- if (x>255)
- return 255;
- else if (x<0)
- return 0;
- else
- return x;
-}
-#endif
-
-/*
- * Perform dequantization and inverse DCT on one block of coefficients.
- */
-
-void
-tinyjpeg_idct_float (struct component *compptr, uint8_t *output_buf, int stride)
-{
- FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
- FAST_FLOAT tmp10, tmp11, tmp12, tmp13;
- FAST_FLOAT z5, z10, z11, z12, z13;
- int16_t *inptr;
- FAST_FLOAT *quantptr;
- FAST_FLOAT *wsptr;
- uint8_t *outptr;
- int ctr;
- FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
-
- /* Pass 1: process columns from input, store into work array. */
-
- inptr = compptr->DCT;
- quantptr = compptr->Q_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;
- outptr = output_buf;
- for (ctr = 0; ctr < DCTSIZE; ctr++) {
- /* 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] = descale_and_clamp((int)(tmp0 + tmp7), 3);
- outptr[7] = descale_and_clamp((int)(tmp0 - tmp7), 3);
- outptr[1] = descale_and_clamp((int)(tmp1 + tmp6), 3);
- outptr[6] = descale_and_clamp((int)(tmp1 - tmp6), 3);
- outptr[2] = descale_and_clamp((int)(tmp2 + tmp5), 3);
- outptr[5] = descale_and_clamp((int)(tmp2 - tmp5), 3);
- outptr[4] = descale_and_clamp((int)(tmp3 + tmp4), 3);
- outptr[3] = descale_and_clamp((int)(tmp3 - tmp4), 3);
-
-
- wsptr += DCTSIZE; /* advance pointer to next row */
- outptr += stride;
- }
-}
-
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