40e6575aa3
This is more spec-compliant because it does not rely on dead-code elimination by the compiler. Especially MSVC has problems with this, as can be seen in https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/296373.html or https://ffmpeg.org/pipermail/ffmpeg-devel/2022-May/297022.html This commit does not eliminate every instance where we rely on dead code elimination: It only tackles branching to the initialization of arch-specific dsp code, not e.g. all uses of CONFIG_ and HAVE_ checks. But maybe it is already enough to compile FFmpeg with MSVC with whole-programm-optimizations enabled (if one does not disable too many components). Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
52 lines
1.7 KiB
C
52 lines
1.7 KiB
C
/*
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* PNG image format
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* Copyright (c) 2008 Loren Merrit <lorenm@u.washington.edu>
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but 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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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "config.h"
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#include "libavutil/attributes.h"
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#include "png.h"
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#include "pngdsp.h"
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// 0x7f7f7f7f or 0x7f7f7f7f7f7f7f7f or whatever, depending on the cpu's native arithmetic size
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#define pb_7f (~0UL / 255 * 0x7f)
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#define pb_80 (~0UL / 255 * 0x80)
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static void add_bytes_l2_c(uint8_t *dst, uint8_t *src1, uint8_t *src2, int w)
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{
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long i;
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for (i = 0; i <= w - (int) sizeof(long); i += sizeof(long)) {
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long a = *(long *)(src1 + i);
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long b = *(long *)(src2 + i);
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*(long *)(dst + i) = ((a & pb_7f) + (b & pb_7f)) ^ ((a ^ b) & pb_80);
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}
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for (; i < w; i++)
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dst[i] = src1[i] + src2[i];
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}
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av_cold void ff_pngdsp_init(PNGDSPContext *dsp)
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{
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dsp->add_bytes_l2 = add_bytes_l2_c;
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dsp->add_paeth_prediction = ff_add_png_paeth_prediction;
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#if ARCH_X86
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ff_pngdsp_init_x86(dsp);
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#endif
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}
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