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-/*
- * 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 */
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