lavc/opusdsp: RISC-V V (128-bit) postfilter

This is implemented for a vector size of 128-bit. Since the scalar
product in the inner loop covers 5 samples or 160 bits, we need a group
multipler of 2.

To avoid reconfiguring the vector type, the outer loop, which loads
multiple input samples sticks to the same multipler. Consequently, the
outer loop loads 8 samples per iteration. This is safe since the minimum
period of the CELT codec is 15 samples.

The same code would also work, albeit needlessly inefficiently with a
vector length of 256 bits. A proper implementation will follow instead.

libavcodec/opusdsp.c

@@ -58,6 +58,8 @@ av_cold void ff_opus_dsp_init(OpusDSP *ctx)
 
 #if ARCH_AARCH64
     ff_opus_dsp_init_aarch64(ctx);
+#elif ARCH_RISCV
+    ff_opus_dsp_init_riscv(ctx);
 #elif ARCH_X86
     ff_opus_dsp_init_x86(ctx);
 #endif

libavcodec/opusdsp.h

@@ -30,5 +30,6 @@ void ff_opus_dsp_init(OpusDSP *ctx);
 
 void ff_opus_dsp_init_x86(OpusDSP *ctx);
 void ff_opus_dsp_init_aarch64(OpusDSP *ctx);
+void ff_opus_dsp_init_riscv(OpusDSP *ctx);
 
 #endif /* AVCODEC_OPUSDSP_H */

libavcodec/riscv/Makefile

@@ -12,6 +12,8 @@ OBJS-$(CONFIG_FMTCONVERT) += riscv/fmtconvert_init.o
 RVV-OBJS-$(CONFIG_FMTCONVERT) += riscv/fmtconvert_rvv.o
 OBJS-$(CONFIG_IDCTDSP) += riscv/idctdsp_init.o
 RVV-OBJS-$(CONFIG_IDCTDSP) += riscv/idctdsp_rvv.o
+OBJS-$(CONFIG_OPUS_DECODER) += riscv/opusdsp_init.o
+RVV-OBJS-$(CONFIG_OPUS_DECODER) += riscv/opusdsp_rvv.o
 OBJS-$(CONFIG_PIXBLOCKDSP) += riscv/pixblockdsp_init.o \
                               riscv/pixblockdsp_rvi.o
 RVV-OBJS-$(CONFIG_PIXBLOCKDSP) += riscv/pixblockdsp_rvv.o

libavcodec/riscv/opusdsp_init.c

@@ -0,0 +1,42 @@
+/*
+ * 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 "libavutil/riscv/cpu.h"
+#include "libavcodec/opusdsp.h"
+
+void ff_opus_postfilter_rvv_128(float *data, int period, float *g, int len);
+
+av_cold void ff_opus_dsp_init_riscv(OpusDSP *d)
+{
+#if HAVE_RVV
+    int flags = av_get_cpu_flags();
+
+    if (flags & AV_CPU_FLAG_RVV_F32)
+        switch (ff_get_rv_vlenb()) {
+        case 16:
+            d->postfilter = ff_opus_postfilter_rvv_128;
+            break;
+        }
+#endif
+}

libavcodec/riscv/opusdsp_rvv.S

@@ -0,0 +1,57 @@
+/*
+ * 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 "libavutil/riscv/asm.S"
+
+func ff_opus_postfilter_rvv_128, zve32f
+        addi         a1, a1, 2
+        slli         a1, a1, 2
+        lw           t1, 4(a2)
+        vsetivli     zero, 3, e32, m1, ta, ma
+        vle32.v      v24, (a2)
+        sub          a1, a0, a1      // a1 = &x4 = &data[-(period + 2)]
+        vsetivli     zero, 5, e32, m2, ta, ma
+        vslide1up.vx v8, v24, t1
+        lw           t2, 8(a2)
+        vle32.v      v16, (a1)
+        vslide1up.vx v24, v8, t2     // v24 = { g[2], g[1], g[0], g[1], g[2] }
+2:
+        vsetvli t0, a3, e32, m2, ta, ma
+        vle32.v v0, (a0)
+        sub     a3, a3, t0
+3:
+        vsetivli       zero, 5, e32, m2, ta, ma
+        lw             t2, 20(a1)
+        vfmul.vv       v8, v24, v16
+        addi           a0, a0, 4
+        vslide1down.vx v16, v16, t2
+        addi           a1, a1, 4
+        vfredusum.vs   v0, v8, v0
+        vsetvli        zero, t0, e32, m2, ta, ma
+        vmv.x.s        t1, v0
+        addi           t0, t0, -1
+        vslide1down.vx v0, v0, zero
+        sw             t1, -4(a0)
+        bnez           t0, 3b
+
+        bnez    a3, 2b
+
+        ret
+endfunc