lavu/riscv: add <intmath.h> optimisations

This provides some micro-optimisations for signed integer clipping, and
support for bit weight with the Zbb extension.

libavutil/intmath.h

@@ -28,8 +28,9 @@
 
 #if ARCH_ARM
 #   include "arm/intmath.h"
-#endif
+#elif ARCH_RISCV
-#if ARCH_X86
+#   include "riscv/intmath.h"
+#elif ARCH_X86
 #   include "x86/intmath.h"
 #endif
 

libavutil/riscv/intmath.h

@@ -0,0 +1,103 @@
+/*
+ * 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
+ */
+
+#ifndef AVUTIL_RISCV_INTMATH_H
+#define AVUTIL_RISCV_INTMATH_H
+
+#include <stdint.h>
+
+#include "config.h"
+#include "libavutil/attributes.h"
+
+/*
+ * The compiler is forced to sign-extend the result anyhow, so it is faster to
+ * compute it explicitly and use it.
+ */
+#define av_clip_int8 av_clip_int8_rvi
+static av_always_inline av_const int8_t av_clip_int8_rvi(int a)
+{
+    union { uint8_t u; int8_t s; } u = { .u = a };
+
+    if (a != u.s)
+        a = ((a >> 31) ^ 0x7F);
+    return a;
+}
+
+#define av_clip_int16 av_clip_int16_rvi
+static av_always_inline av_const int16_t av_clip_int16_rvi(int a)
+{
+    union { uint8_t u; int8_t s; } u = { .u = a };
+
+    if (a != u.s)
+        a = ((a >> 31) ^ 0x7F);
+    return a;
+}
+
+#define av_clipl_int32 av_clipl_int32_rvi
+static av_always_inline av_const int32_t av_clipl_int32_rvi(int64_t a)
+{
+    union { uint32_t u; int32_t s; } u = { .u = a };
+
+    if (a != u.s)
+        a = ((a >> 63) ^ 0x7FFFFFFF);
+    return a;
+}
+
+#define av_clip_intp2 av_clip_intp2_rvi
+static av_always_inline av_const int av_clip_intp2_rvi(int a, int p)
+{
+    const int shift = 32 - p;
+    int b = (a << shift) >> shift;
+
+    if (a != b)
+        b = (a >> 31) ^ ((1 << p) - 1);
+    return b;
+}
+
+#if defined (__riscv_zbb) && (__riscv_zbb > 0) && HAVE_INLINE_ASM
+
+#define av_popcount av_popcount_rvb
+static av_always_inline av_const int av_popcount_rvb(uint32_t x)
+{
+    int ret;
+
+#if (__riscv_xlen >= 64)
+    __asm__ ("cpopw %0, %1\n" : "=r" (ret) : "r" (x));
+#else
+    __asm__ ("cpop %0, %1\n" : "=r" (ret) : "r" (x));
+#endif
+    return ret;
+}
+
+#if (__riscv_xlen >= 64)
+#define av_popcount64 av_popcount64_rvb
+static av_always_inline av_const int av_popcount64_rvb(uint64_t x)
+{
+    int ret;
+
+#if (__riscv_xlen >= 128)
+    __asm__ ("cpopd %0, %1\n" : "=r" (ret) : "r" (x));
+#else
+    __asm__ ("cpop %0, %1\n" : "=r" (ret) : "r" (x));
+#endif
+    return ret;
+}
+#endif /* __riscv_xlen >= 64 */
+#endif /* __riscv_zbb */
+
+#endif /* AVUTIL_RISCV_INTMATH_H */