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The loop iterates over the length of the vector, not the order. This is
to avoid reloading the same data for each lag value. However this means
the loop only works if the maximum order is no larger than VLENB.
The loop is roughly equivalent to:
for (size_t j = 0; j < lag; j++)
autoc[j] = 1.;
while (len > lag) {
for (ptrdiff_t j = 0; j < lag; j++)
autoc[j] += data[j] * *data;
data++;
len--;
}
while (len > 0) {
for (ptrdiff_t j = 0; j < len; j++)
autoc[j] += data[j] * *data;
data++;
len--;
}
Since register pressure is only at 50%, it should be possible to implement
the same loop for order up to 2xVLENB. But this is left for future work.
Performance numbers are all over the place from ~1.25x to ~4x speedups,
but at least they are always noticeably better than nothing.
44 lines
1.5 KiB
C
44 lines
1.5 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 "config.h"
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#include "libavutil/attributes.h"
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#include "libavutil/cpu.h"
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#include "libavutil/riscv/cpu.h"
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#include "libavcodec/lpc.h"
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void ff_lpc_apply_welch_window_rvv(const int32_t *, ptrdiff_t, double *);
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void ff_lpc_compute_autocorr_rvv(const double *, ptrdiff_t, int, double *);
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av_cold void ff_lpc_init_riscv(LPCContext *c)
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{
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#if HAVE_RVV && (__riscv_xlen >= 64)
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int flags = av_get_cpu_flags();
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if ((flags & AV_CPU_FLAG_RVV_F64) && (flags & AV_CPU_FLAG_RVB_ADDR)) {
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c->lpc_apply_welch_window = ff_lpc_apply_welch_window_rvv;
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if (ff_get_rv_vlenb() >= c->max_order)
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c->lpc_compute_autocorr = ff_lpc_compute_autocorr_rvv;
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}
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#endif
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}
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