f0ef11ea83
Simply taking the Zbb REV8 instruction into use in a simple loop gives some significant savings: bswap_buf_c: 1081.0 bswap_buf_rvb_b: 771.0 But we can also use the 64-bit REV8 as a pseudo-SIMD instruction with just one additional shift, and one fewer load, effectively doubling the bandwidth. Consequently, this patch is useful even if the compile-time target has Zbb enabled for C code: bswap_buf_c: 1081.0 bswap_buf_rvb_b: 341.0 (this patch) On the other hand, this approach fails miserably for bswap16_buf as the ratio of shifts and stores becomes unfavorable compared to naïve C: bswap16_buf_c: 1542.0 bswap16_buf_rvb_b: 1803.7 Unrolling to process 128 bits (4 samples) at a time actually worsens performance ever so slightly: bswap_buf_c: 1081.0 bswap_buf_rvb_b: 408.5
39 lines
1.2 KiB
C
39 lines
1.2 KiB
C
/*
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* Copyright © 2022 Rémi Denis-Courmont.
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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 <stdint.h>
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#include "config.h"
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#include "libavutil/attributes.h"
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#include "libavutil/cpu.h"
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#include "libavcodec/bswapdsp.h"
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void ff_bswap32_buf_rvb(uint32_t *dst, const uint32_t *src, int len);
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av_cold void ff_bswapdsp_init_riscv(BswapDSPContext *c)
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{
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#if (__riscv_xlen >= 64)
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int cpu_flags = av_get_cpu_flags();
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if (cpu_flags & AV_CPU_FLAG_RVB_BASIC)
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c->bswap_buf = ff_bswap32_buf_rvb;
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#endif
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}
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