125 lines
3.4 KiB
C
125 lines
3.4 KiB
C
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/*
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* This module is specialized to the case DCTSIZE = 8.
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*/
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#include "cjpeg.h"
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/*
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* Perform the forward DCT on one block of samples.
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*/
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void
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jpeg_fdct(float *data)
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{
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float tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;
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float tmp10, tmp11, tmp12, tmp13;
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float z1, z2, z3, z4, z5, z11, z13;
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float *dataptr;
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int ctr;
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/* Pass 1: process rows. */
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dataptr = data;
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for (ctr = 0; ctr < DCTSIZE; ctr++) {
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/* Load data into workspace */
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tmp0 = dataptr[0] + dataptr[7];
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tmp7 = dataptr[0] - dataptr[7];
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tmp1 = dataptr[1] + dataptr[6];
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tmp6 = dataptr[1] - dataptr[6];
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tmp2 = dataptr[2] + dataptr[5];
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tmp5 = dataptr[2] - dataptr[5];
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tmp3 = dataptr[3] + dataptr[4];
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tmp4 = dataptr[3] - dataptr[4];
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/* Even part */
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tmp10 = tmp0 + tmp3; /* phase 2 */
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tmp13 = tmp0 - tmp3;
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tmp11 = tmp1 + tmp2;
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tmp12 = tmp1 - tmp2;
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/* Apply unsigned->signed conversion */
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dataptr[0] = tmp10 + tmp11; /* phase 3 */
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dataptr[4] = tmp10 - tmp11;
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z1 = (tmp12 + tmp13) * ((float) 0.707106781); /* c4 */
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dataptr[2] = tmp13 + z1; /* phase 5 */
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dataptr[6] = tmp13 - z1;
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/* Odd part */
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tmp10 = tmp4 + tmp5; /* phase 2 */
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tmp11 = tmp5 + tmp6;
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tmp12 = tmp6 + tmp7;
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/* The rotator is modified from fig 4-8 to avoid extra negations. */
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z5 = (tmp10 - tmp12) * ((float) 0.382683433); /* c6 */
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z2 = ((float) 0.541196100) * tmp10 + z5; /* c2-c6 */
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z4 = ((float) 1.306562965) * tmp12 + z5; /* c2+c6 */
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z3 = tmp11 * ((float) 0.707106781); /* c4 */
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z11 = tmp7 + z3; /* phase 5 */
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z13 = tmp7 - z3;
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dataptr[5] = z13 + z2; /* phase 6 */
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dataptr[3] = z13 - z2;
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dataptr[1] = z11 + z4;
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dataptr[7] = z11 - z4;
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dataptr += DCTSIZE; /* advance pointer to next row */
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}
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/* Pass 2: process columns. */
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dataptr = data;
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for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {
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tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];
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tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];
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tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];
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tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];
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tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];
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tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];
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tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];
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tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];
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/* Even part */
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tmp10 = tmp0 + tmp3; /* phase 2 */
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tmp13 = tmp0 - tmp3;
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tmp11 = tmp1 + tmp2;
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tmp12 = tmp1 - tmp2;
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dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */
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dataptr[DCTSIZE*4] = tmp10 - tmp11;
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z1 = (tmp12 + tmp13) * ((float) 0.707106781); /* c4 */
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dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */
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dataptr[DCTSIZE*6] = tmp13 - z1;
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/* Odd part */
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tmp10 = tmp4 + tmp5; /* phase 2 */
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tmp11 = tmp5 + tmp6;
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tmp12 = tmp6 + tmp7;
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/* The rotator is modified from fig 4-8 to avoid extra negations. */
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z5 = (tmp10 - tmp12) * ((float) 0.382683433); /* c6 */
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z2 = ((float) 0.541196100) * tmp10 + z5; /* c2-c6 */
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z4 = ((float) 1.306562965) * tmp12 + z5; /* c2+c6 */
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z3 = tmp11 * ((float) 0.707106781); /* c4 */
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z11 = tmp7 + z3; /* phase 5 */
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z13 = tmp7 - z3;
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dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */
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dataptr[DCTSIZE*3] = z13 - z2;
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dataptr[DCTSIZE*1] = z11 + z4;
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dataptr[DCTSIZE*7] = z11 - z4;
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dataptr++; /* advance pointer to next column */
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}
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}
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