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Justine Tunney 2020-06-15 07:18:57 -07:00
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "dsp/core/core.h"
#define DCT(A, B, C, D, E, F, G, H, T, C0, C1, C2, C3, C4) \
do { \
T z1, z2, z3, z4, z5, z11, z13; \
T t0, t1, t2, t3, t4, t5, t6, t7, t8, t10, t11, t12, t13; \
t0 = A + H; \
t7 = A - H; \
t1 = B + G; \
t6 = B - G; \
t2 = C + F; \
t5 = C - F; \
t3 = D + E; \
t4 = D - E; \
t10 = t0 + t3; \
t13 = t0 - t3; \
t11 = t1 + t2; \
t12 = t1 - t2; \
A = t10 + t11; \
E = t10 - t11; \
z1 = (t12 + t13) * C0; \
C = t13 + z1; \
G = t13 - z1; \
t10 = t4 + t5; \
t11 = t5 + t6; \
t12 = t6 + t7; \
z5 = (t10 - t12) * C1; \
z2 = t10 * C2 + z5; \
z4 = t12 * C3 + z5; \
z3 = t11 * C4; \
z11 = t7 + z3; \
z13 = t7 - z3; \
F = z13 + z2; \
D = z13 - z2; \
B = z11 + z4; \
H = z11 - z4; \
} while (0)
/**
* Performs float forward discrete cosine transform.
*
* This takes a tiny block of image data and shoves the information it
* represents into the top left corner. It can be reversed using idct().
* It matters because iterating the result in a serpentine pattern makes
* run-length delta encoding super effective. Furthermore, data downward
* rightly may be divided away for lossy compression.
*
* @cost ~100ns
*/
void *dct(float M[8][8], float c0, float c1, float c2, float c3, float c4) {
unsigned y, x;
for (y = 0; y < 8; ++y) {
DCT(M[y][0], M[y][1], M[y][2], M[y][3], M[y][4], M[y][5], M[y][6], M[y][7],
float, c0, c1, c2, c3, c4);
}
for (x = 0; x < 8; ++x) {
DCT(M[0][x], M[1][x], M[2][x], M[3][x], M[4][x], M[5][x], M[6][x], M[7][x],
float, c0, c1, c2, c3, c4);
}
return M;
}
void *dctjpeg(float M[8][8]) {
return dct(M, .707106781f, .382683433f, .541196100f, 1.306562965f,
.707106781f);
}