lavc/alacdsp: RISC-V V decorrelate_stereo

To avoid data dependencies, this does the following unroll, which
requires one extra but probably free addition:

    coeff = (b * left_weight) >> decorr_shift;
    b += a;
    a -= coeff;
    b -= coeff;
    swap(a, b);

1 files changed, 39 insertions, 0 deletions

diff --git a/libavcodec/riscv/alacdsp_init.c b/libavcodec/riscv/alacdsp_init.c
new file mode 100644
index 0000000000..9ddebaa60b
--- /dev/null
+++ b/libavcodec/riscv/alacdsp_init.c
@@ -0,0 +1,39 @@
+/*
+ * 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 <stdint.h>
+
+#include "libavutil/attributes.h"
+#include "libavutil/cpu.h"
+#include "libavcodec/avcodec.h"
+#include "libavcodec/alacdsp.h"
+
+void ff_alac_decorrelate_stereo_rvv(int32_t *buffer[2], int nb_samples,
+                                    int decorr_shift, int decorr_left_weight);
+
+av_cold void ff_alacdsp_init_riscv(ALACDSPContext *c)
+{
+#if HAVE_RVV && (__riscv_xlen == 64)
+    int flags = av_get_cpu_flags();
+
+    if (flags & AV_CPU_FLAG_RVV_I32)
+        c->decorrelate_stereo = ff_alac_decorrelate_stereo_rvv;
+#endif
+}