lavc/lpc: R-V V apply_welch_window

apply_welch_window_even_c:       617.5
apply_welch_window_even_rvv_f64: 235.0
apply_welch_window_odd_c:        709.0
apply_welch_window_odd_rvv_f64:  256.5

libavcodec/riscv/lpc_init.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright © 2022 Rémi Denis-Courmont.
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "config.h"
+
+#include "libavutil/attributes.h"
+#include "libavutil/cpu.h"
+#include "libavcodec/lpc.h"
+
+void ff_lpc_apply_welch_window_rvv(const int32_t *, ptrdiff_t, double *);
+
+av_cold void ff_lpc_init_riscv(LPCContext *c)
+{
+#if HAVE_RVV && (__riscv_xlen >= 64)
+    int flags = av_get_cpu_flags();
+
+    if ((flags & AV_CPU_FLAG_RVV_F64) && (flags & AV_CPU_FLAG_RVB_ADDR))
+        c->lpc_apply_welch_window = ff_lpc_apply_welch_window_rvv;
+#endif
+}