+++ /dev/null
-/*
- * jidctint.c
- *
- * Copyright (C) 1991-1998, 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 slow-but-accurate integer implementation of the
- * inverse DCT (Discrete Cosine Transform). In the IJG code, this routine
- * must also perform dequantization of the input coefficients.
- *
- * 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 an algorithm described in
- * C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
- * Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
- * Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
- * The primary algorithm described there uses 11 multiplies and 29 adds.
- * We use their alternate method with 12 multiplies and 32 adds.
- * The advantage of this method is that no data path contains more than one
- * multiplication; this allows a very simple and accurate implementation in
- * scaled fixed-point arithmetic, with a minimal number of shifts.
- */
-
-#define JPEG_INTERNALS
-#include "jinclude.h"
-#include "jpeglib.h"
-#include "jdct.h" /* Private declarations for DCT subsystem */
-
-#ifdef DCT_ISLOW_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
-
-
-/*
- * The poop on this scaling stuff is as follows:
- *
- * Each 1-D IDCT step produces outputs which are a factor of sqrt(N)
- * larger than the true IDCT outputs. The final outputs are therefore
- * a factor of N larger than desired; since N=8 this can be cured by
- * a simple right shift at the end of the algorithm. The advantage of
- * this arrangement is that we save two multiplications per 1-D IDCT,
- * because the y0 and y4 inputs need not be divided by sqrt(N).
- *
- * We have to do addition and subtraction of the integer inputs, which
- * is no problem, and multiplication by fractional constants, which is
- * a problem to do in integer arithmetic. We multiply all the constants
- * by CONST_SCALE and convert them to integer constants (thus retaining
- * CONST_BITS bits of precision in the constants). After doing a
- * multiplication we have to divide the product by CONST_SCALE, with proper
- * rounding, to produce the correct output. This division can be done
- * cheaply as a right shift of CONST_BITS bits. We postpone shifting
- * as long as possible so that partial sums can be added together with
- * full fractional precision.
- *
- * The outputs of the first pass are scaled up by PASS1_BITS bits so that
- * they are represented to better-than-integral precision. These outputs
- * require BITS_IN_JSAMPLE + PASS1_BITS + 3 bits; this fits in a 16-bit word
- * with the recommended scaling. (To scale up 12-bit sample data further, an
- * intermediate INT32 array would be needed.)
- *
- * To avoid overflow of the 32-bit intermediate results in pass 2, we must
- * have BITS_IN_JSAMPLE + CONST_BITS + PASS1_BITS <= 26. Error analysis
- * shows that the values given below are the most effective.
- */
-
-#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_298631336 ((INT32) 2446) /* FIX(0.298631336) */
-#define FIX_0_390180644 ((INT32) 3196) /* FIX(0.390180644) */
-#define FIX_0_541196100 ((INT32) 4433) /* FIX(0.541196100) */
-#define FIX_0_765366865 ((INT32) 6270) /* FIX(0.765366865) */
-#define FIX_0_899976223 ((INT32) 7373) /* FIX(0.899976223) */
-#define FIX_1_175875602 ((INT32) 9633) /* FIX(1.175875602) */
-#define FIX_1_501321110 ((INT32) 12299) /* FIX(1.501321110) */
-#define FIX_1_847759065 ((INT32) 15137) /* FIX(1.847759065) */
-#define FIX_1_961570560 ((INT32) 16069) /* FIX(1.961570560) */
-#define FIX_2_053119869 ((INT32) 16819) /* FIX(2.053119869) */
-#define FIX_2_562915447 ((INT32) 20995) /* FIX(2.562915447) */
-#define FIX_3_072711026 ((INT32) 25172) /* FIX(3.072711026) */
-#else
-#define FIX_0_298631336 FIX(0.298631336)
-#define FIX_0_390180644 FIX(0.390180644)
-#define FIX_0_541196100 FIX(0.541196100)
-#define FIX_0_765366865 FIX(0.765366865)
-#define FIX_0_899976223 FIX(0.899976223)
-#define FIX_1_175875602 FIX(1.175875602)
-#define FIX_1_501321110 FIX(1.501321110)
-#define FIX_1_847759065 FIX(1.847759065)
-#define FIX_1_961570560 FIX(1.961570560)
-#define FIX_2_053119869 FIX(2.053119869)
-#define FIX_2_562915447 FIX(2.562915447)
-#define FIX_3_072711026 FIX(3.072711026)
-#endif
-
-
-/* Multiply an INT32 variable by an INT32 constant to yield an INT32 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.
- */
-
-GLOBAL(void)
-jpeg_idct_islow (j_decompress_ptr cinfo, jpeg_component_info * compptr,
- JCOEFPTR coef_block,
- JSAMPARRAY output_buf, JDIMENSION output_col)
-{
- INT32 tmp0, tmp1, tmp2, tmp3;
- INT32 tmp10, tmp11, tmp12, tmp13;
- INT32 z1, z2, z3, z4, z5;
- JCOEFPTR inptr;
- ISLOW_MULT_TYPE * quantptr;
- int * wsptr;
- JSAMPROW outptr;
- JSAMPLE *range_limit = IDCT_range_limit(cinfo);
- int ctr;
- int workspace[DCTSIZE2]; /* buffers data between passes */
- SHIFT_TEMPS
-
- /* Pass 1: process columns from input, store into work array. */
- /* Note results are scaled up by sqrt(8) compared to a true IDCT; */
- /* furthermore, we scale the results by 2**PASS1_BITS. */
-
- inptr = coef_block;
- quantptr = (ISLOW_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 */
- int dcval = 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;
- 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: reverse the even part of the forward DCT. */
- /* The rotator is sqrt(2)*c(-6). */
-
- z2 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2]);
- z3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6]);
-
- z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
- tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
- tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
-
- z2 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0]);
- z3 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4]);
-
- tmp0 = (z2 + z3) << CONST_BITS;
- tmp1 = (z2 - z3) << CONST_BITS;
-
- tmp10 = tmp0 + tmp3;
- tmp13 = tmp0 - tmp3;
- tmp11 = tmp1 + tmp2;
- tmp12 = tmp1 - tmp2;
-
- /* Odd part per figure 8; the matrix is unitary and hence its
- * transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively.
- */
-
- tmp0 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7]);
- tmp1 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5]);
- tmp2 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3]);
- tmp3 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1]);
-
- z1 = tmp0 + tmp3;
- z2 = tmp1 + tmp2;
- z3 = tmp0 + tmp2;
- z4 = tmp1 + tmp3;
- z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
-
- tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
- tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
- tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
- tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
- z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
- z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
- z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
- z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
-
- z3 += z5;
- z4 += z5;
-
- tmp0 += z1 + z3;
- tmp1 += z2 + z4;
- tmp2 += z2 + z3;
- tmp3 += z1 + z4;
-
- /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
-
- wsptr[DCTSIZE*0] = (int) DESCALE(tmp10 + tmp3, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*7] = (int) DESCALE(tmp10 - tmp3, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*1] = (int) DESCALE(tmp11 + tmp2, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*6] = (int) DESCALE(tmp11 - tmp2, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*2] = (int) DESCALE(tmp12 + tmp1, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*5] = (int) DESCALE(tmp12 - tmp1, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*3] = (int) DESCALE(tmp13 + tmp0, CONST_BITS-PASS1_BITS);
- wsptr[DCTSIZE*4] = (int) DESCALE(tmp13 - tmp0, CONST_BITS-PASS1_BITS);
-
- 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, */
- /* and also undo the PASS1_BITS scaling. */
-
- 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).
- * On machines with very fast multiplication, it's possible that the
- * test takes more time than it's worth. In that case this section
- * may be commented out.
- */
-
-#ifndef NO_ZERO_ROW_TEST
- if (wsptr[1] == 0 && wsptr[2] == 0 && wsptr[3] == 0 && wsptr[4] == 0 &&
- wsptr[5] == 0 && wsptr[6] == 0 && wsptr[7] == 0) {
- /* AC terms all zero */
- JSAMPLE dcval = range_limit[(int) DESCALE((INT32) wsptr[0], PASS1_BITS+3)
- & RANGE_MASK];
-
- outptr[0] = dcval;
- outptr[1] = dcval;
- outptr[2] = dcval;
- outptr[3] = dcval;
- outptr[4] = dcval;
- outptr[5] = dcval;
- outptr[6] = dcval;
- outptr[7] = dcval;
-
- wsptr += DCTSIZE; /* advance pointer to next row */
- continue;
- }
-#endif
-
- /* Even part: reverse the even part of the forward DCT. */
- /* The rotator is sqrt(2)*c(-6). */
-
- z2 = (INT32) wsptr[2];
- z3 = (INT32) wsptr[6];
-
- z1 = MULTIPLY(z2 + z3, FIX_0_541196100);
- tmp2 = z1 + MULTIPLY(z3, - FIX_1_847759065);
- tmp3 = z1 + MULTIPLY(z2, FIX_0_765366865);
-
- tmp0 = ((INT32) wsptr[0] + (INT32) wsptr[4]) << CONST_BITS;
- tmp1 = ((INT32) wsptr[0] - (INT32) wsptr[4]) << CONST_BITS;
-
- tmp10 = tmp0 + tmp3;
- tmp13 = tmp0 - tmp3;
- tmp11 = tmp1 + tmp2;
- tmp12 = tmp1 - tmp2;
-
- /* Odd part per figure 8; the matrix is unitary and hence its
- * transpose is its inverse. i0..i3 are y7,y5,y3,y1 respectively.
- */
-
- tmp0 = (INT32) wsptr[7];
- tmp1 = (INT32) wsptr[5];
- tmp2 = (INT32) wsptr[3];
- tmp3 = (INT32) wsptr[1];
-
- z1 = tmp0 + tmp3;
- z2 = tmp1 + tmp2;
- z3 = tmp0 + tmp2;
- z4 = tmp1 + tmp3;
- z5 = MULTIPLY(z3 + z4, FIX_1_175875602); /* sqrt(2) * c3 */
-
- tmp0 = MULTIPLY(tmp0, FIX_0_298631336); /* sqrt(2) * (-c1+c3+c5-c7) */
- tmp1 = MULTIPLY(tmp1, FIX_2_053119869); /* sqrt(2) * ( c1+c3-c5+c7) */
- tmp2 = MULTIPLY(tmp2, FIX_3_072711026); /* sqrt(2) * ( c1+c3+c5-c7) */
- tmp3 = MULTIPLY(tmp3, FIX_1_501321110); /* sqrt(2) * ( c1+c3-c5-c7) */
- z1 = MULTIPLY(z1, - FIX_0_899976223); /* sqrt(2) * (c7-c3) */
- z2 = MULTIPLY(z2, - FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
- z3 = MULTIPLY(z3, - FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
- z4 = MULTIPLY(z4, - FIX_0_390180644); /* sqrt(2) * (c5-c3) */
-
- z3 += z5;
- z4 += z5;
-
- tmp0 += z1 + z3;
- tmp1 += z2 + z4;
- tmp2 += z2 + z3;
- tmp3 += z1 + z4;
-
- /* Final output stage: inputs are tmp10..tmp13, tmp0..tmp3 */
-
- outptr[0] = range_limit[(int) DESCALE(tmp10 + tmp3,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[7] = range_limit[(int) DESCALE(tmp10 - tmp3,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[1] = range_limit[(int) DESCALE(tmp11 + tmp2,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[6] = range_limit[(int) DESCALE(tmp11 - tmp2,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[2] = range_limit[(int) DESCALE(tmp12 + tmp1,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[5] = range_limit[(int) DESCALE(tmp12 - tmp1,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[3] = range_limit[(int) DESCALE(tmp13 + tmp0,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
- outptr[4] = range_limit[(int) DESCALE(tmp13 - tmp0,
- CONST_BITS+PASS1_BITS+3)
- & RANGE_MASK];
-
- wsptr += DCTSIZE; /* advance pointer to next row */
- }
-}
-
-#endif /* DCT_ISLOW_SUPPORTED */
projects / opencv / blobdiff