[RVV] Enable Scale{ARGB,UV}RowDown{2,4,EVEN}_RVV

Run on SiFive internal FPGA:

Test case               RVV function				Speedup
I444ScaleDownBy3_Box	ScaleAddRow_RVV+ScaleAddCols(scalar)	2.8
ARGBScaleDownBy2_None	ScaleARGBRowDown2_RVV		        2.2
ARGBScaleDownBy2_Linear	ScaleARGBRowDown2Linear_RVV		5.0
ARGBScaleDownBy2_Box	ScaleARGBRowDown2Box_RVV		4.3
ARGBScaleDownBy4_None	ScaleARGBRowDownEven_RVV		1.2
ARGBScaleDownBy8_Box	ScaleARGBRowDownEvenBox_RVV		3.2
ARGBScaleDownBy4_Box	ScaleARGBRowDown2Box_RVV		4.5
I444ScaleDownBy2_None	ScaleRowDown2_RVV			5.8
I444ScaleDownBy2_Linear	ScaleRowDown2Linear_RVV			6.1
I444ScaleDownBy2_Box	ScaleRowDown2Box_RVV			5.0
I444ScaleDownBy4_None	ScaleRowDown4_RVV			3.6
I444ScaleDownBy4_Box	ScaleRowDown4Box_RVV			3.5
UVScaleDownBy2_None	ScaleUVRowDown2_RVV			5.8
UVScaleDownBy2_Linear	ScaleUVRowDown2Linear_RVV		5.6
UVScaleDownBy2_Box	ScaleUVRowDown2Box_RVV			4.1
UVScaleDownBy4_None	ScaleUVRowDown4_RVV			1.7
UVScaleDownBy4_Box	ScaleUVRowDown2Box_RVV			4.5
						avg-speedup:    4

Note: Specialize ScaleUVRowDown with step_size=4 by ScaleUVRowDown4_RVV.

Bug: libyuv:956
Change-Id: If9604a6aadf681193f282507602c57c726332202
Signed-off-by: Darren Hsieh <darren.hsieh@sifive.com>
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/4601684
Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>

6 files changed, 612 insertions, 0 deletions

diff --git a/include/libyuv/scale_row.h b/include/libyuv/scale_row.h
index a7957c3f..631b15dd 100644
--- a/include/libyuv/scale_row.h
+++ b/include/libyuv/scale_row.h
@@ -175,6 +175,18 @@ extern "C" {
 #define HAS_SCALEROWDOWN34_LSX
 #endif
 
+#if !defined(LIBYUV_DISABLE_RVV) && defined(__riscv_vector)
+#define HAS_SCALEADDROW_RVV
+#define HAS_SCALEARGBROWDOWN2_RVV
+#define HAS_SCALEARGBROWDOWNEVEN_RVV
+#define HAS_SCALEROWDOWN2_RVV
+#define HAS_SCALEROWDOWN4_RVV
+#define HAS_SCALEUVROWDOWN2_RVV
+#define HAS_SCALEUVROWDOWN2LINEAR_RVV
+#define HAS_SCALEUVROWDOWN2BOX_RVV
+#define HAS_SCALEUVROWDOWNEVEN_RVV
+#endif
+
 // Scale ARGB vertically with bilinear interpolation.
 void ScalePlaneVertical(int src_height,
                         int dst_width,
@@ -949,6 +961,18 @@ void ScaleARGBRowDown2Box_NEON(const uint8_t* src_ptr,
                                ptrdiff_t src_stride,
                                uint8_t* dst,
                                int dst_width);
+void ScaleARGBRowDown2_RVV(const uint8_t* src_argb,
+                           ptrdiff_t src_stride,
+                           uint8_t* dst_argb,
+                           int dst_width);
+void ScaleARGBRowDown2Linear_RVV(const uint8_t* src_argb,
+                                 ptrdiff_t src_stride,
+                                 uint8_t* dst_argb,
+                                 int dst_width);
+void ScaleARGBRowDown2Box_RVV(const uint8_t* src_argb,
+                              ptrdiff_t src_stride,
+                              uint8_t* dst_argb,
+                              int dst_width);
 void ScaleARGBRowDown2_MSA(const uint8_t* src_argb,
                            ptrdiff_t src_stride,
                            uint8_t* dst_argb,
@@ -1061,6 +1085,16 @@ void ScaleARGBRowDownEvenBox_LSX(const uint8_t* src_argb,
                                  int src_stepx,
                                  uint8_t* dst_argb,
                                  int dst_width);
+void ScaleARGBRowDownEven_RVV(const uint8_t* src_argb,
+                              ptrdiff_t src_stride,
+                              int32_t src_stepx,
+                              uint8_t* dst_argb,
+                              int dst_width);
+void ScaleARGBRowDownEvenBox_RVV(const uint8_t* src_argb,
+                                 ptrdiff_t src_stride,
+                                 int src_stepx,
+                                 uint8_t* dst_argb,
+                                 int dst_width);
 void ScaleARGBRowDownEven_Any_SSE2(const uint8_t* src_ptr,
                                    ptrdiff_t src_stride,
                                    int src_stepx,
@@ -1143,6 +1177,18 @@ void ScaleUVRowDown2Box_MSA(const uint8_t* src_ptr,
                             ptrdiff_t src_stride,
                             uint8_t* dst_uv,
                             int dst_width);
+void ScaleUVRowDown2_RVV(const uint8_t* src_ptr,
+                         ptrdiff_t src_stride,
+                         uint8_t* dst_uv,
+                         int dst_width);
+void ScaleUVRowDown2Linear_RVV(const uint8_t* src_ptr,
+                               ptrdiff_t src_stride,
+                               uint8_t* dst_uv,
+                               int dst_width);
+void ScaleUVRowDown2Box_RVV(const uint8_t* src_ptr,
+                            ptrdiff_t src_stride,
+                            uint8_t* dst,
+                            int dst_width);
 void ScaleUVRowDown2_Any_SSSE3(const uint8_t* src_ptr,
                                ptrdiff_t src_stride,
                                uint8_t* dst_ptr,
@@ -1203,6 +1249,16 @@ void ScaleUVRowDownEvenBox_NEON(const uint8_t* src_ptr,
                                 int src_stepx,
                                 uint8_t* dst_uv,
                                 int dst_width);
+void ScaleUVRowDown4_RVV(const uint8_t* src_ptr,
+                         ptrdiff_t src_stride,
+                         int32_t src_stepx,
+                         uint8_t* dst_uv,
+                         int dst_width);
+void ScaleUVRowDownEven_RVV(const uint8_t* src_ptr,
+                            ptrdiff_t src_stride,
+                            int32_t src_stepx,
+                            uint8_t* dst_uv,
+                            int dst_width);
 void ScaleUVRowDownEven_MSA(const uint8_t* src_ptr,
                             ptrdiff_t src_stride,
                             int32_t src_stepx,
@@ -1744,6 +1800,29 @@ void ScaleRowDown34_1_Box_Any_LSX(const uint8_t* src_ptr,
                                   uint8_t* dst_ptr,
                                   int dst_width);
 
+void ScaleAddRow_RVV(const uint8_t* src_ptr, uint16_t* dst_ptr, int src_width);
+void ScaleRowDown2_RVV(const uint8_t* src_ptr,
+                       ptrdiff_t src_stride,
+                       uint8_t* dst,
+                       int dst_width);
+void ScaleRowDown2Linear_RVV(const uint8_t* src_ptr,
+                             ptrdiff_t src_stride,
+                             uint8_t* dst,
+                             int dst_width);
+void ScaleRowDown2Box_RVV(const uint8_t* src_ptr,
+                          ptrdiff_t src_stride,
+                          uint8_t* dst,
+                          int dst_width);
+
+void ScaleRowDown4_RVV(const uint8_t* src_ptr,
+                       ptrdiff_t src_stride,
+                       uint8_t* dst_ptr,
+                       int dst_width);
+void ScaleRowDown4Box_RVV(const uint8_t* src_ptr,
+                          ptrdiff_t src_stride,
+                          uint8_t* dst_ptr,
+                          int dst_width);
+
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
diff --git a/source/rotate_argb.cc b/source/rotate_argb.cc
index c7239010..034d53e8 100644
--- a/source/rotate_argb.cc
+++ b/source/rotate_argb.cc
@@ -69,6 +69,11 @@ static int ARGBTranspose(const uint8_t* src_argb,
     }
   }
 #endif
+#if defined(HAS_SCALEARGBROWDOWNEVEN_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleARGBRowDownEven = ScaleARGBRowDownEven_RVV;
+  }
+#endif
 
   for (i = 0; i < width; ++i) {  // column of source to row of dest.
     ScaleARGBRowDownEven(src_argb, 0, src_pixel_step, dst_argb, height);
diff --git a/source/scale.cc b/source/scale.cc
index 80b030dc..1cda2234 100644
--- a/source/scale.cc
+++ b/source/scale.cc
@@ -135,6 +135,14 @@ static void ScalePlaneDown2(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEROWDOWN2_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleRowDown2 = filtering == kFilterNone
+                        ? ScaleRowDown2_RVV
+                        : (filtering == kFilterLinear ? ScaleRowDown2Linear_RVV
+                                                      : ScaleRowDown2Box_RVV);
+  }
+#endif
 
   if (filtering == kFilterLinear) {
     src_stride = 0;
@@ -312,6 +320,11 @@ static void ScalePlaneDown4(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEROWDOWN4_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleRowDown4 = filtering ? ScaleRowDown4Box_RVV : ScaleRowDown4_RVV;
+  }
+#endif
 
   if (filtering == kFilterLinear) {
     src_stride = 0;
@@ -971,6 +984,11 @@ static void ScalePlaneBox(int src_width,
       }
     }
 #endif
+#if defined(HAS_SCALEADDROW_RVV)
+    if (TestCpuFlag(kCpuHasRVV)) {
+      ScaleAddRow = ScaleAddRow_RVV;
+    }
+#endif
 
     for (j = 0; j < dst_height; ++j) {
       int boxheight;
diff --git a/source/scale_argb.cc b/source/scale_argb.cc
index ddd8d29e..214f932c 100644
--- a/source/scale_argb.cc
+++ b/source/scale_argb.cc
@@ -127,6 +127,15 @@ static void ScaleARGBDown2(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEARGBROWDOWN2_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleARGBRowDown2 =
+        filtering == kFilterNone
+            ? ScaleARGBRowDown2_RVV
+            : (filtering == kFilterLinear ? ScaleARGBRowDown2Linear_RVV
+                                          : ScaleARGBRowDown2Box_RVV);
+  }
+#endif
 
   if (filtering == kFilterLinear) {
     src_stride = 0;
@@ -184,6 +193,11 @@ static void ScaleARGBDown4Box(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEARGBROWDOWN2_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleARGBRowDown2 = ScaleARGBRowDown2Box_RVV;
+  }
+#endif
 
   for (j = 0; j < dst_height; ++j) {
     ScaleARGBRowDown2(src_argb, src_stride, row, dst_width * 2);
@@ -263,6 +277,12 @@ static void ScaleARGBDownEven(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEARGBROWDOWNEVEN_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleARGBRowDownEven =
+        filtering ? ScaleARGBRowDownEvenBox_RVV : ScaleARGBRowDownEven_RVV;
+  }
+#endif
 
   if (filtering == kFilterLinear) {
     src_stride = 0;
diff --git a/source/scale_rvv.cc b/source/scale_rvv.cc
new file mode 100644
index 00000000..a045ec17
--- /dev/null
+++ b/source/scale_rvv.cc
@@ -0,0 +1,470 @@
+/*
+ *  Copyright 2023 The LibYuv Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS. All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+/*
+ * Copyright (c) 2023 SiFive, Inc. All rights reserved.
+ *
+ * Contributed by Darren Hsieh <darren.hsieh@sifive.com>
+ * Contributed by Bruce Lai <bruce.lai@sifive.com>
+ */
+
+#include "libyuv/row.h"
+#include "libyuv/scale_row.h"
+
+// This module is for gcc/clang rvv.
+#if !defined(LIBYUV_DISABLE_RVV) && defined(__riscv_vector)
+#include <riscv_vector.h>
+
+#ifdef __cplusplus
+namespace libyuv {
+extern "C" {
+#endif
+
+void ScaleAddRow_RVV(const uint8_t* src_ptr, uint16_t* dst_ptr, int src_width) {
+  size_t w = (size_t)src_width;
+  do {
+    size_t vl = __riscv_vsetvl_e8m4(w);
+    vuint8m4_t v_src = __riscv_vle8_v_u8m4(src_ptr, vl);
+    vuint16m8_t v_dst = __riscv_vle16_v_u16m8(dst_ptr, vl);
+    // Use widening multiply-add instead of widening + add
+    v_dst = __riscv_vwmaccu_vx_u16m8(v_dst, 1, v_src, vl);
+    __riscv_vse16_v_u16m8(dst_ptr, v_dst, vl);
+    w -= vl;
+    src_ptr += vl;
+    dst_ptr += vl;
+  } while (w > 0);
+}
+
+void ScaleARGBRowDown2_RVV(const uint8_t* src_argb,
+                           ptrdiff_t src_stride,
+                           uint8_t* dst_argb,
+                           int dst_width) {
+  (void)src_stride;
+  size_t w = (size_t)dst_width;
+  const uint64_t* src = (const uint64_t*)(src_argb);
+  uint32_t* dst = (uint32_t*)(dst_argb);
+  do {
+    vuint64m8_t v_data;
+    vuint32m4_t v_dst;
+    size_t vl = __riscv_vsetvl_e64m8(w);
+    v_data = __riscv_vle64_v_u64m8(src, vl);
+    v_dst = __riscv_vnsrl_wx_u32m4(v_data, 32, vl);
+    __riscv_vse32_v_u32m4(dst, v_dst, vl);
+    w -= vl;
+    src += vl;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleARGBRowDown2Linear_RVV(const uint8_t* src_argb,
+                                 ptrdiff_t src_stride,
+                                 uint8_t* dst_argb,
+                                 int dst_width) {
+  (void)src_stride;
+  size_t w = (size_t)dst_width;
+  const uint32_t* src = (const uint32_t*)(src_argb);
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m4_t v_odd, v_even, v_dst;
+    vuint16m8_t v_sum;
+    vuint32m4_t v_odd_32, v_even_32;
+    size_t vl = __riscv_vsetvl_e32m4(w);
+    __riscv_vlseg2e32_v_u32m4(&v_even_32, &v_odd_32, src, vl);
+    v_even = __riscv_vreinterpret_v_u32m4_u8m4(v_even_32);
+    v_odd = __riscv_vreinterpret_v_u32m4_u8m4(v_odd_32);
+    // Use round-to-nearest-up mode for averaging add
+    v_dst = __riscv_vaaddu_vv_u8m4(v_even, v_odd, vl * 4);
+    __riscv_vse8_v_u8m4(dst_argb, v_dst, vl * 4);
+    w -= vl;
+    src += vl * 2;
+    dst_argb += vl * 4;
+  } while (w > 0);
+}
+
+void ScaleARGBRowDown2Box_RVV(const uint8_t* src_argb,
+                              ptrdiff_t src_stride,
+                              uint8_t* dst_argb,
+                              int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint32_t* src0 = (const uint32_t*)(src_argb);
+  const uint32_t* src1 = (const uint32_t*)(src_argb + src_stride);
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m4_t v_row0_odd, v_row0_even, v_row1_odd, v_row1_even, v_dst;
+    vuint16m8_t v_row0_sum, v_row1_sum, v_dst_16;
+    vuint32m4_t v_row0_odd_32, v_row0_even_32, v_row1_odd_32, v_row1_even_32;
+    size_t vl = __riscv_vsetvl_e32m4(w);
+    __riscv_vlseg2e32_v_u32m4(&v_row0_even_32, &v_row0_odd_32, src0, vl);
+    __riscv_vlseg2e32_v_u32m4(&v_row1_even_32, &v_row1_odd_32, src1, vl);
+    v_row0_even = __riscv_vreinterpret_v_u32m4_u8m4(v_row0_even_32);
+    v_row0_odd = __riscv_vreinterpret_v_u32m4_u8m4(v_row0_odd_32);
+    v_row1_even = __riscv_vreinterpret_v_u32m4_u8m4(v_row1_even_32);
+    v_row1_odd = __riscv_vreinterpret_v_u32m4_u8m4(v_row1_odd_32);
+    v_row0_sum = __riscv_vwaddu_vv_u16m8(v_row0_even, v_row0_odd, vl * 4);
+    v_row1_sum = __riscv_vwaddu_vv_u16m8(v_row1_even, v_row1_odd, vl * 4);
+    v_dst_16 = __riscv_vadd_vv_u16m8(v_row0_sum, v_row1_sum, vl * 4);
+    // Use round-to-nearest-up mode for vnclip
+    v_dst = __riscv_vnclipu_wx_u8m4(v_dst_16, 2, vl * 4);
+    __riscv_vse8_v_u8m4(dst_argb, v_dst, vl * 4);
+    w -= vl;
+    src0 += vl * 2;
+    src1 += vl * 2;
+    dst_argb += vl * 4;
+  } while (w > 0);
+}
+
+void ScaleARGBRowDownEven_RVV(const uint8_t* src_argb,
+                              ptrdiff_t src_stride,
+                              int src_stepx,
+                              uint8_t* dst_argb,
+                              int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint32_t* src = (const uint32_t*)(src_argb);
+  uint32_t* dst = (uint32_t*)(dst_argb);
+  const int stride_byte = src_stepx * 4;
+  do {
+    vuint32m8_t v_row;
+    size_t vl = __riscv_vsetvl_e32m8(w);
+    v_row = __riscv_vlse32_v_u32m8(src, stride_byte, vl);
+    __riscv_vse32_v_u32m8(dst, v_row, vl);
+    w -= vl;
+    src += vl * src_stepx;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleARGBRowDownEvenBox_RVV(const uint8_t* src_argb,
+                                 ptrdiff_t src_stride,
+                                 int src_stepx,
+                                 uint8_t* dst_argb,
+                                 int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint32_t* src0 = (const uint32_t*)(src_argb);
+  const uint32_t* src1 = (const uint32_t*)(src_argb + src_stride);
+  const int stride_byte = src_stepx * 4;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m4_t v_row0_low, v_row0_high, v_row1_low, v_row1_high, v_dst;
+    vuint16m8_t v_row0_sum, v_row1_sum, v_sum;
+    vuint32m4_t v_row0_low_32, v_row0_high_32, v_row1_low_32, v_row1_high_32;
+    size_t vl = __riscv_vsetvl_e32m4(w);
+    __riscv_vlsseg2e32_v_u32m4(&v_row0_low_32, &v_row0_high_32, src0,
+                               stride_byte, vl);
+    __riscv_vlsseg2e32_v_u32m4(&v_row1_low_32, &v_row1_high_32, src1,
+                               stride_byte, vl);
+    v_row0_low = __riscv_vreinterpret_v_u32m4_u8m4(v_row0_low_32);
+    v_row0_high = __riscv_vreinterpret_v_u32m4_u8m4(v_row0_high_32);
+    v_row1_low = __riscv_vreinterpret_v_u32m4_u8m4(v_row1_low_32);
+    v_row1_high = __riscv_vreinterpret_v_u32m4_u8m4(v_row1_high_32);
+    v_row0_sum = __riscv_vwaddu_vv_u16m8(v_row0_low, v_row0_high, vl * 4);
+    v_row1_sum = __riscv_vwaddu_vv_u16m8(v_row1_low, v_row1_high, vl * 4);
+    v_sum = __riscv_vadd_vv_u16m8(v_row0_sum, v_row1_sum, vl * 4);
+    // Use round-to-nearest-up mode for vnclip
+    v_dst = __riscv_vnclipu_wx_u8m4(v_sum, 2, vl * 4);
+    __riscv_vse8_v_u8m4(dst_argb, v_dst, vl * 4);
+    w -= vl;
+    src0 += vl * src_stepx;
+    src1 += vl * src_stepx;
+    dst_argb += vl * 4;
+  } while (w > 0);
+}
+
+void ScaleRowDown2_RVV(const uint8_t* src_ptr,
+                       ptrdiff_t src_stride,
+                       uint8_t* dst,
+                       int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint16_t* src = (const uint16_t*)src_ptr;
+  (void)src_stride;
+  do {
+    size_t vl = __riscv_vsetvl_e16m8(w);
+    vuint16m8_t v_src = __riscv_vle16_v_u16m8(src, vl);
+    vuint8m4_t v_dst = __riscv_vnsrl_wx_u8m4(v_src, 8, vl);
+    __riscv_vse8_v_u8m4(dst, v_dst, vl);
+    w -= vl;
+    src += vl;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleRowDown2Linear_RVV(const uint8_t* src_ptr,
+                             ptrdiff_t src_stride,
+                             uint8_t* dst,
+                             int dst_width) {
+  size_t w = (size_t)dst_width;
+  (void)src_stride;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m4_t v_s0, v_s1, v_dst;
+    size_t vl = __riscv_vsetvl_e8m4(w);
+    __riscv_vlseg2e8_v_u8m4(&v_s0, &v_s1, src_ptr, vl);
+    // Use round-to-nearest-up mode for averaging add
+    v_dst = __riscv_vaaddu_vv_u8m4(v_s0, v_s1, vl);
+    __riscv_vse8_v_u8m4(dst, v_dst, vl);
+    w -= vl;
+    src_ptr += 2 * vl;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleRowDown2Box_RVV(const uint8_t* src_ptr,
+                          ptrdiff_t src_stride,
+                          uint8_t* dst,
+                          int dst_width) {
+  const uint8_t* s = src_ptr;
+  const uint8_t* t = src_ptr + src_stride;
+  size_t w = (size_t)dst_width;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    size_t vl = __riscv_vsetvl_e8m4(w);
+    vuint8m4_t v_s0, v_s1, v_t0, v_t1;
+    vuint16m8_t v_s01, v_t01, v_st01;
+    vuint8m4_t v_dst;
+    __riscv_vlseg2e8_v_u8m4(&v_s0, &v_s1, s, vl);
+    __riscv_vlseg2e8_v_u8m4(&v_t0, &v_t1, t, vl);
+    v_s01 = __riscv_vwaddu_vv_u16m8(v_s0, v_s1, vl);
+    v_t01 = __riscv_vwaddu_vv_u16m8(v_t0, v_t1, vl);
+    v_st01 = __riscv_vadd_vv_u16m8(v_s01, v_t01, vl);
+    // Use round-to-nearest-up mode for vnclip
+    v_dst = __riscv_vnclipu_wx_u8m4(v_st01, 2, vl);
+    __riscv_vse8_v_u8m4(dst, v_dst, vl);
+    w -= vl;
+    s += 2 * vl;
+    t += 2 * vl;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleRowDown4_RVV(const uint8_t* src_ptr,
+                       ptrdiff_t src_stride,
+                       uint8_t* dst_ptr,
+                       int dst_width) {
+  size_t w = (size_t)dst_width;
+  (void)src_stride;
+  do {
+    size_t vl = __riscv_vsetvl_e8m2(w);
+    vuint8m2_t v_s0, v_s1, v_s2, v_s3;
+    __riscv_vlseg4e8_v_u8m2(&v_s0, &v_s1, &v_s2, &v_s3, src_ptr, vl);
+    __riscv_vse8_v_u8m2(dst_ptr, v_s2, vl);
+    w -= vl;
+    src_ptr += (4 * vl);
+    dst_ptr += vl;
+  } while (w > 0);
+}
+
+void ScaleRowDown4Box_RVV(const uint8_t* src_ptr,
+                          ptrdiff_t src_stride,
+                          uint8_t* dst_ptr,
+                          int dst_width) {
+  const uint8_t* src_ptr1 = src_ptr + src_stride;
+  const uint8_t* src_ptr2 = src_ptr + src_stride * 2;
+  const uint8_t* src_ptr3 = src_ptr + src_stride * 3;
+  size_t w = (size_t)dst_width;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m2_t v_s0, v_s1, v_s2, v_s3;
+    vuint8m2_t v_t0, v_t1, v_t2, v_t3;
+    vuint8m2_t v_u0, v_u1, v_u2, v_u3;
+    vuint8m2_t v_v0, v_v1, v_v2, v_v3;
+    vuint16m4_t v_s01, v_s23, v_t01, v_t23;
+    vuint16m4_t v_u01, v_u23, v_v01, v_v23;
+    vuint16m4_t v_st01, v_st23, v_uv01, v_uv23;
+    vuint16m4_t v_st0123, v_uv0123, v_stuv0123;
+    vuint8m2_t v_dst;
+    size_t vl = __riscv_vsetvl_e8m2(w);
+
+    __riscv_vlseg4e8_v_u8m2(&v_s0, &v_s1, &v_s2, &v_s3, src_ptr, vl);
+    v_s01 = __riscv_vwaddu_vv_u16m4(v_s0, v_s1, vl);
+
+    __riscv_vlseg4e8_v_u8m2(&v_t0, &v_t1, &v_t2, &v_t3, src_ptr1, vl);
+    v_t01 = __riscv_vwaddu_vv_u16m4(v_t0, v_t1, vl);
+
+    __riscv_vlseg4e8_v_u8m2(&v_u0, &v_u1, &v_u2, &v_u3, src_ptr2, vl);
+    v_u01 = __riscv_vwaddu_vv_u16m4(v_u0, v_u1, vl);
+    v_u23 = __riscv_vwaddu_vv_u16m4(v_u2, v_u3, vl);
+
+    v_s23 = __riscv_vwaddu_vv_u16m4(v_s2, v_s3, vl);
+    v_t23 = __riscv_vwaddu_vv_u16m4(v_t2, v_t3, vl);
+    v_st01 = __riscv_vadd_vv_u16m4(v_s01, v_t01, vl);
+    v_st23 = __riscv_vadd_vv_u16m4(v_s23, v_t23, vl);
+
+    __riscv_vlseg4e8_v_u8m2(&v_v0, &v_v1, &v_v2, &v_v3, src_ptr3, vl);
+
+    v_v01 = __riscv_vwaddu_vv_u16m4(v_v0, v_v1, vl);
+    v_v23 = __riscv_vwaddu_vv_u16m4(v_v2, v_v3, vl);
+
+    v_uv01 = __riscv_vadd_vv_u16m4(v_u01, v_v01, vl);
+    v_uv23 = __riscv_vadd_vv_u16m4(v_u23, v_v23, vl);
+
+    v_st0123 = __riscv_vadd_vv_u16m4(v_st01, v_st23, vl);
+    v_uv0123 = __riscv_vadd_vv_u16m4(v_uv01, v_uv23, vl);
+    v_stuv0123 = __riscv_vadd_vv_u16m4(v_st0123, v_uv0123, vl);
+    // Use round-to-nearest-up mode for vnclip
+    v_dst = __riscv_vnclipu_wx_u8m2(v_stuv0123, 4, vl);
+    __riscv_vse8_v_u8m2(dst_ptr, v_dst, vl);
+    w -= vl;
+    src_ptr += 4 * vl;
+    src_ptr1 += 4 * vl;
+    src_ptr2 += 4 * vl;
+    src_ptr3 += 4 * vl;
+    dst_ptr += vl;
+  } while (w > 0);
+}
+
+void ScaleUVRowDown2_RVV(const uint8_t* src_uv,
+                         ptrdiff_t src_stride,
+                         uint8_t* dst_uv,
+                         int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint32_t* src = (const uint32_t*)src_uv;
+  uint16_t* dst = (uint16_t*)dst_uv;
+  (void)src_stride;
+  do {
+    size_t vl = __riscv_vsetvl_e32m8(w);
+    vuint32m8_t v_data = __riscv_vle32_v_u32m8(src, vl);
+    vuint16m4_t v_u1v1 = __riscv_vnsrl_wx_u16m4(v_data, 16, vl);
+    __riscv_vse16_v_u16m4(dst, v_u1v1, vl);
+    w -= vl;
+    src += vl;
+    dst += vl;
+  } while (w > 0);
+}
+
+void ScaleUVRowDown2Linear_RVV(const uint8_t* src_uv,
+                               ptrdiff_t src_stride,
+                               uint8_t* dst_uv,
+                               int dst_width) {
+  size_t w = (size_t)dst_width;
+  const uint16_t* src = (const uint16_t*)src_uv;
+  (void)src_stride;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m4_t v_u0v0, v_u1v1, v_avg;
+    vuint16m4_t v_u0v0_16, v_u1v1_16;
+    size_t vl = __riscv_vsetvl_e16m4(w);
+    vlseg2e16_v_u16m4(&v_u0v0_16, &v_u1v1_16, src, vl);
+    v_u0v0 = __riscv_vreinterpret_v_u16m4_u8m4(v_u0v0_16);
+    v_u1v1 = __riscv_vreinterpret_v_u16m4_u8m4(v_u1v1_16);
+    // Use round-to-nearest-up mode for averaging add
+    v_avg = __riscv_vaaddu_vv_u8m4(v_u0v0, v_u1v1, vl * 2);
+    __riscv_vse8_v_u8m4(dst_uv, v_avg, vl * 2);
+    w -= vl;
+    src += vl * 2;
+    dst_uv += vl * 2;
+  } while (w > 0);
+}
+
+void ScaleUVRowDown2Box_RVV(const uint8_t* src_uv,
+                            ptrdiff_t src_stride,
+                            uint8_t* dst_uv,
+                            int dst_width) {
+  const uint8_t* src_uv_row1 = src_uv + src_stride;
+  size_t w = (size_t)dst_width;
+  // NOTE: To match behavior on other platforms, vxrm (fixed-point rounding mode
+  // register) is set to round-to-nearest-up mode(0).
+  asm volatile("csrwi vxrm, 0");
+  do {
+    vuint8m2_t v_u0_row0, v_v0_row0, v_u1_row0, v_v1_row0;
+    vuint8m2_t v_u0_row1, v_v0_row1, v_u1_row1, v_v1_row1;
+    vuint16m4_t v_u0u1_row0, v_u0u1_row1, v_v0v1_row0, v_v0v1_row1;
+    vuint16m4_t v_sum0, v_sum1;
+    vuint8m2_t v_dst_u, v_dst_v;
+    size_t vl = __riscv_vsetvl_e8m2(w);
+
+    __riscv_vlseg4e8_v_u8m2(&v_u0_row0, &v_v0_row0, &v_u1_row0, &v_v1_row0,
+                            src_uv, vl);
+    __riscv_vlseg4e8_v_u8m2(&v_u0_row1, &v_v0_row1, &v_u1_row1, &v_v1_row1,
+                            src_uv_row1, vl);
+
+    v_u0u1_row0 = __riscv_vwaddu_vv_u16m4(v_u0_row0, v_u1_row0, vl);
+    v_u0u1_row1 = __riscv_vwaddu_vv_u16m4(v_u0_row1, v_u1_row1, vl);
+    v_v0v1_row0 = __riscv_vwaddu_vv_u16m4(v_v0_row0, v_v1_row0, vl);
+    v_v0v1_row1 = __riscv_vwaddu_vv_u16m4(v_v0_row1, v_v1_row1, vl);
+
+    v_sum0 = __riscv_vadd_vv_u16m4(v_u0u1_row0, v_u0u1_row1, vl);
+    v_sum1 = __riscv_vadd_vv_u16m4(v_v0v1_row0, v_v0v1_row1, vl);
+    // Use round-to-nearest-up mode for vnclip
+    v_dst_u = __riscv_vnclipu_wx_u8m2(v_sum0, 2, vl);
+    v_dst_v = __riscv_vnclipu_wx_u8m2(v_sum1, 2, vl);
+
+    __riscv_vsseg2e8_v_u8m2(dst_uv, v_dst_u, v_dst_v, vl);
+
+    dst_uv += 2 * vl;
+    src_uv += 4 * vl;
+    w -= vl;
+    src_uv_row1 += 4 * vl;
+  } while (w > 0);
+}
+
+void ScaleUVRowDown4_RVV(const uint8_t* src_uv,
+                         ptrdiff_t src_stride,
+                         int src_stepx,
+                         uint8_t* dst_uv,
+                         int dst_width) {
+  // Overflow will never happen here, since sizeof(size_t)/sizeof(int)=2.
+  // dst_width = src_width / 4 and src_width is also int.
+  size_t w = (size_t)dst_width * 8;
+  (void)src_stride;
+  (void)src_stepx;
+  do {
+    size_t vl = __riscv_vsetvl_e8m8(w);
+    vuint8m8_t v_row = __riscv_vle8_v_u8m8(src_uv, vl);
+    vuint64m8_t v_row_64 = __riscv_vreinterpret_v_u8m8_u64m8(v_row);
+    // Narrowing without clipping
+    vuint32m4_t v_tmp = __riscv_vncvt_x_x_w_u32m4(v_row_64, vl / 8);
+    vuint16m2_t v_dst_16 = __riscv_vncvt_x_x_w_u16m2(v_tmp, vl / 8);
+    vuint8m2_t v_dst = __riscv_vreinterpret_v_u16m2_u8m2(v_dst_16);
+    __riscv_vse8_v_u8m2(dst_uv, v_dst, vl / 4);
+    w -= vl;
+    src_uv += vl;
+    dst_uv += vl / 4;
+  } while (w > 0);
+}
+
+void ScaleUVRowDownEven_RVV(const uint8_t* src_uv,
+                            ptrdiff_t src_stride,
+                            int src_stepx,
+                            uint8_t* dst_uv,
+                            int dst_width) {
+  size_t w = (size_t)dst_width;
+  const ptrdiff_t stride_byte = (ptrdiff_t)src_stepx * 2;
+  const uint16_t* src = (const uint16_t*)(src_uv);
+  uint16_t* dst = (uint16_t*)(dst_uv);
+  (void)src_stride;
+  do {
+    size_t vl = __riscv_vsetvl_e16m8(w);
+    vuint16m8_t v_row = __riscv_vlse16_v_u16m8(src, stride_byte, vl);
+    __riscv_vse16_v_u16m8(dst, v_row, vl);
+    w -= vl;
+    src += vl * src_stepx;
+    dst += vl;
+  } while (w > 0);
+}
+
+#ifdef __cplusplus
+}  // extern "C"
+}  // namespace libyuv
+#endif
+
+#endif  // !defined(LIBYUV_DISABLE_RVV) && defined(__riscv_vector)
diff --git a/source/scale_uv.cc b/source/scale_uv.cc
index 1556071d..5246f8f6 100644
--- a/source/scale_uv.cc
+++ b/source/scale_uv.cc
@@ -128,6 +128,15 @@ static void ScaleUVDown2(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEUVROWDOWN2_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleUVRowDown2 =
+        filtering == kFilterNone
+            ? ScaleUVRowDown2_RVV
+            : (filtering == kFilterLinear ? ScaleUVRowDown2Linear_RVV
+                                          : ScaleUVRowDown2Box_RVV);
+  }
+#endif
 
 // This code is not enabled.  Only box filter is available at this time.
 #if defined(HAS_SCALEUVROWDOWN2_SSSE3)
@@ -231,6 +240,11 @@ static void ScaleUVDown4Box(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEUVROWDOWN2BOX_RVV)
+  if (TestCpuFlag(kCpuHasRVV)) {
+    ScaleUVRowDown2 = ScaleUVRowDown2Box_RVV;
+  }
+#endif
 
   for (j = 0; j < dst_height; ++j) {
     ScaleUVRowDown2(src_uv, src_stride, row, dst_width * 2);
@@ -310,6 +324,12 @@ static void ScaleUVDownEven(int src_width,
     }
   }
 #endif
+#if defined(HAS_SCALEUVROWDOWNEVEN_RVV)
+  if (TestCpuFlag(kCpuHasRVV) && !filtering) {
+    ScaleUVRowDownEven =
+        (col_step == 4) ? ScaleUVRowDown4_RVV : ScaleUVRowDownEven_RVV;
+  }
+#endif
 
   if (filtering == kFilterLinear) {
     src_stride = 0;