58 lines
3.2 KiB
C
58 lines
3.2 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/limits.h"
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#include "libc/log/check.h"
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#include "libc/log/log.h"
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#include "libc/macros.h"
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#include "libc/str/str.h"
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#include "third_party/stb/internal.h"
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/* this is a reduced-precision calculation of YCbCr-to-RGB introduced
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to make sure the code produces the same results in both SIMD and scalar */
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#define FLOAT2FIXED(x) (((int)((x)*4096.0f + .5f)) << 8)
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void stbi__YCbCr_to_RGB_row(unsigned char *out, const unsigned char *y,
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const unsigned char *pcb, const unsigned char *pcr,
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unsigned count, unsigned step) {
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unsigned i;
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unsigned char b4[4];
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int y_fixed, r, g, b, cr, cb;
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CHECK(step == 3 || step == 4);
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CHECK_LE(count, INT_MAX / 4 - 4);
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for (i = step == 4 ? stbi__YCbCr_to_RGB_row$sse2(out, y, pcb, pcr, count) : 0;
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i < count; ++i) {
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y_fixed = (y[i] << 20) + (1 << 19); /* rounding */
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cr = pcr[i] - 128;
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cb = pcb[i] - 128;
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r = y_fixed + cr * FLOAT2FIXED(1.40200f);
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g = y_fixed + (cr * -FLOAT2FIXED(0.71414f)) +
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((cb * -FLOAT2FIXED(0.34414f)) & 0xffff0000);
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b = y_fixed + cb * FLOAT2FIXED(1.77200f);
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r >>= 20;
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g >>= 20;
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b >>= 20;
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b4[0] = MIN(255, MAX(0, r));
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b4[1] = MIN(255, MAX(0, g));
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b4[2] = MIN(255, MAX(0, b));
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b4[3] = 255;
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memcpy(out + i * step, b4, 4);
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}
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}
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