Port the more accurate (and slightly faster) floating point IDCT implementation from jpeg-8a and later. New research revealed that the SSE/SSE2 floating point IDCT implementation was actually more accurate than the jpeg-6b implementation, not less, which is why its mathematical results have always differed from those of the jpeg-6b implementation. This patch brings the accuracy of the C code in line with that of the SSE/SSE2 code.
This commit is contained in:
DRC
79
jidctflt.c
79
jidctflt.c
@@ -1,9 +1,12 @@
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/*
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* jidctflt.c
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*
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* This file was part of the Independent JPEG Group's software:
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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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* For conditions of distribution and use, see the accompanying README file.
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* Modified 2010 by Guido Vollbeding.
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* libjpeg-turbo Modifications:
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* Copyright (C) 2014, D. R. Commander.
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* For conditions of distribution and use, see the accompanying README file.
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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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@@ -76,10 +79,10 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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FLOAT_MULT_TYPE * quantptr;
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FAST_FLOAT * wsptr;
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JSAMPROW outptr;
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JSAMPLE *range_limit = IDCT_range_limit(cinfo);
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JSAMPLE *range_limit = cinfo->sample_range_limit;
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int ctr;
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FAST_FLOAT workspace[DCTSIZE2]; /* buffers data between passes */
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SHIFT_TEMPS
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#define _0_125 ((FLOAT_MULT_TYPE)0.125)
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/* Pass 1: process columns from input, store into work array. */
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@@ -101,7 +104,8 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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FAST_FLOAT dcval = DEQUANTIZE(inptr[DCTSIZE*0],
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quantptr[DCTSIZE*0] * _0_125);
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wsptr[DCTSIZE*0] = dcval;
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wsptr[DCTSIZE*1] = dcval;
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@@ -120,10 +124,10 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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tmp0 = DEQUANTIZE(inptr[DCTSIZE*0], quantptr[DCTSIZE*0] * _0_125);
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tmp1 = DEQUANTIZE(inptr[DCTSIZE*2], quantptr[DCTSIZE*2] * _0_125);
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tmp2 = DEQUANTIZE(inptr[DCTSIZE*4], quantptr[DCTSIZE*4] * _0_125);
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tmp3 = DEQUANTIZE(inptr[DCTSIZE*6], quantptr[DCTSIZE*6] * _0_125);
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tmp10 = tmp0 + tmp2; /* phase 3 */
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tmp11 = tmp0 - tmp2;
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@@ -138,10 +142,10 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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tmp4 = DEQUANTIZE(inptr[DCTSIZE*1], quantptr[DCTSIZE*1] * _0_125);
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tmp5 = DEQUANTIZE(inptr[DCTSIZE*3], quantptr[DCTSIZE*3] * _0_125);
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tmp6 = DEQUANTIZE(inptr[DCTSIZE*5], quantptr[DCTSIZE*5] * _0_125);
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tmp7 = DEQUANTIZE(inptr[DCTSIZE*7], quantptr[DCTSIZE*7] * _0_125);
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z13 = tmp6 + tmp5; /* phase 6 */
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z10 = tmp6 - tmp5;
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@@ -152,12 +156,12 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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tmp10 = z5 - z12 * ((FAST_FLOAT) 1.082392200); /* 2*(c2-c6) */
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tmp12 = z5 - z10 * ((FAST_FLOAT) 2.613125930); /* 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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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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@@ -165,8 +169,8 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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wsptr[DCTSIZE*3] = tmp3 + tmp4;
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wsptr[DCTSIZE*4] = tmp3 - tmp4;
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inptr++; /* advance pointers to next column */
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quantptr++;
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@@ -174,7 +178,6 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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for (ctr = 0; ctr < DCTSIZE; ctr++) {
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@@ -187,8 +190,10 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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/* Apply signed->unsigned and prepare float->int conversion */
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z5 = wsptr[0] + ((FAST_FLOAT) CENTERJSAMPLE + (FAST_FLOAT) 0.5);
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tmp10 = z5 + wsptr[4];
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tmp11 = z5 - 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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@@ -209,31 +214,23 @@ jpeg_idct_float (j_decompress_ptr cinfo, jpeg_component_info * compptr,
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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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tmp10 = z5 - z12 * ((FAST_FLOAT) 1.082392200); /* 2*(c2-c6) */
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tmp12 = z5 - z10 * ((FAST_FLOAT) 2.613125930); /* 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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tmp4 = tmp10 - tmp5;
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/* Final output stage: scale down by a factor of 8 and range-limit */
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/* Final output stage: float->int conversion and range-limit */
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outptr[0] = range_limit[(int) DESCALE((INT32) (tmp0 + tmp7), 3)
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& RANGE_MASK];
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outptr[7] = range_limit[(int) DESCALE((INT32) (tmp0 - tmp7), 3)
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& RANGE_MASK];
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outptr[1] = range_limit[(int) DESCALE((INT32) (tmp1 + tmp6), 3)
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& RANGE_MASK];
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outptr[6] = range_limit[(int) DESCALE((INT32) (tmp1 - tmp6), 3)
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& RANGE_MASK];
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outptr[2] = range_limit[(int) DESCALE((INT32) (tmp2 + tmp5), 3)
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& RANGE_MASK];
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outptr[5] = range_limit[(int) DESCALE((INT32) (tmp2 - tmp5), 3)
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& RANGE_MASK];
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outptr[4] = range_limit[(int) DESCALE((INT32) (tmp3 + tmp4), 3)
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& RANGE_MASK];
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outptr[3] = range_limit[(int) DESCALE((INT32) (tmp3 - tmp4), 3)
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& RANGE_MASK];
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outptr[0] = range_limit[((int) (tmp0 + tmp7)) & RANGE_MASK];
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outptr[7] = range_limit[((int) (tmp0 - tmp7)) & RANGE_MASK];
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outptr[1] = range_limit[((int) (tmp1 + tmp6)) & RANGE_MASK];
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outptr[6] = range_limit[((int) (tmp1 - tmp6)) & RANGE_MASK];
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outptr[2] = range_limit[((int) (tmp2 + tmp5)) & RANGE_MASK];
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outptr[5] = range_limit[((int) (tmp2 - tmp5)) & RANGE_MASK];
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outptr[3] = range_limit[((int) (tmp3 + tmp4)) & RANGE_MASK];
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outptr[4] = range_limit[((int) (tmp3 - tmp4)) & RANGE_MASK];
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wsptr += DCTSIZE; /* advance pointer to next row */
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}
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