Merge pull request opencv#26624 from hanliutong:rvv-mean

Add RISC-V HAL implementation for meanStdDev opencv#26624

`meanStdDev` benefits from the Universal Intrinsic backend of RVV, but we also found that the performance on the `8UC4` type is worse than the scalar version when there is a mask, and there is no optimization implementation on `32FC1`.

This patch implements `meanStdDev` function in RVV_HAL using native intrinsic, significantly optimizing the performance for `8UC1`, `8UC4` and `32FC1`.

This patch is tested on BPI-F3 for both gcc 14.2 and clang 19.1.
```
$ opencv_test_core --gtest_filter="*MeanStdDev*"
$ opencv_perf_core --gtest_filter="Size_MatType_meanStdDev*
```

![1734077611879](https://github.com/user-attachments/assets/71c85c9d-1db1-470d-81d1-bf546e27ad86)

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [ ] The PR is proposed to the proper branch
- [ ] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

Author: hanliutong

3rdparty/hal_rvv/hal_rvv.hpp

@@ -21,6 +21,7 @@
 
 #if defined(__riscv_v) && __riscv_v == 1000000
 #include "hal_rvv_1p0/merge.hpp" // core
+#include "hal_rvv_1p0/mean.hpp" // core
 #endif
 
 #endif

3rdparty/hal_rvv/hal_rvv_1p0/mean.hpp

@@ -0,0 +1,228 @@
+// This file is part of OpenCV project.
+// It is subject to the license terms in the LICENSE file found in the top-level directory
+// of this distribution and at http://opencv.org/license.html.
+#ifndef OPENCV_HAL_RVV_MEANSTDDEV_HPP_INCLUDED
+#define OPENCV_HAL_RVV_MEANSTDDEV_HPP_INCLUDED
+
+#include <riscv_vector.h>
+
+namespace cv { namespace cv_hal_rvv {
+
+#undef cv_hal_meanStdDev
+#define cv_hal_meanStdDev cv::cv_hal_rvv::meanStdDev
+
+inline int meanStdDev_8UC1(const uchar* src_data, size_t src_step, int width, int height,
+                            double* mean_val, double* stddev_val, uchar* mask, size_t mask_step);
+inline int meanStdDev_8UC4(const uchar* src_data, size_t src_step, int width, int height,
+                            double* mean_val, double* stddev_val, uchar* mask, size_t mask_step);
+inline int meanStdDev_32FC1(const uchar* src_data, size_t src_step, int width, int height,
+                            double* mean_val, double* stddev_val, uchar* mask, size_t mask_step);
+
+inline int meanStdDev(const uchar* src_data, size_t src_step, int width, int height,
+                             int src_type, double* mean_val, double* stddev_val, uchar* mask, size_t mask_step) {
+    switch (src_type)
+    {
+    case CV_8UC1:
+        return meanStdDev_8UC1(src_data, src_step, width, height, mean_val, stddev_val, mask, mask_step);
+    case CV_8UC4:
+        return meanStdDev_8UC4(src_data, src_step, width, height, mean_val, stddev_val, mask, mask_step);
+    case CV_32FC1:
+        return meanStdDev_32FC1(src_data, src_step, width, height, mean_val, stddev_val, mask, mask_step);
+    default:
+        return CV_HAL_ERROR_NOT_IMPLEMENTED;
+    }
+}
+
+inline int meanStdDev_8UC1(const uchar* src_data, size_t src_step, int width, int height,
+                             double* mean_val, double* stddev_val, uchar* mask, size_t mask_step) {
+    int nz = 0;
+    int vlmax = __riscv_vsetvlmax_e64m8();
+    vuint64m8_t vec_sum = __riscv_vmv_v_x_u64m8(0, vlmax);
+    vuint64m8_t vec_sqsum = __riscv_vmv_v_x_u64m8(0, vlmax);
+    if (mask) {
+        for (int i = 0; i < height; ++i) {
+            const uchar* src_row = src_data + i * src_step;
+            const uchar* mask_row = mask + i * mask_step;
+            int j = 0, vl;
+            for ( ; j < width; j += vl) {
+                vl = __riscv_vsetvl_e8m1(width - j);
+                auto vec_pixel_u8 = __riscv_vle8_v_u8m1(src_row + j, vl);
+                auto vmask_u8 = __riscv_vle8_v_u8m1(mask_row+j, vl);
+                auto vec_pixel = __riscv_vzext_vf4(vec_pixel_u8, vl);
+                auto vmask = __riscv_vmseq_vx_u8m1_b8(vmask_u8, 1, vl);
+                vec_sum = __riscv_vwaddu_wv_u64m8_tumu(vmask, vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vwmaccu_vv_u64m8_tumu(vmask, vec_sqsum, vec_pixel, vec_pixel, vl);
+                nz += __riscv_vcpop_m_b8(vmask, vl);
+            }
+        }
+    } else {
+        for (int i = 0; i < height; i++) {
+            const uchar*  src_row = src_data + i * src_step;
+            int j = 0, vl;
+            for ( ; j < width; j += vl) {
+                vl = __riscv_vsetvl_e8m1(width - j);
+                auto vec_pixel_u8 = __riscv_vle8_v_u8m1(src_row + j, vl);
+                auto vec_pixel = __riscv_vzext_vf4(vec_pixel_u8, vl);
+                vec_sum = __riscv_vwaddu_wv_u64m8_tu(vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vwmaccu_vv_u64m8_tu(vec_sqsum, vec_pixel, vec_pixel, vl);
+            }
+        }
+        nz = height * width;
+    }
+    if (nz == 0) {
+        if (mean_val) *mean_val = 0.0;
+        if (stddev_val) *stddev_val = 0.0;
+        return CV_HAL_ERROR_OK;
+    }
+    auto zero = __riscv_vmv_s_x_u64m1(0, vlmax);
+    auto vec_red = __riscv_vmv_v_x_u64m1(0, vlmax);
+    auto vec_reddev = __riscv_vmv_v_x_u64m1(0, vlmax);
+    vec_red = __riscv_vredsum(vec_sum, zero, vlmax);
+    vec_reddev = __riscv_vredsum(vec_sqsum, zero, vlmax);
+    double sum = __riscv_vmv_x(vec_red);
+    double mean = sum / nz;
+    if (mean_val) {
+        *mean_val = mean;
+    }
+    if (stddev_val) {
+        double sqsum = __riscv_vmv_x(vec_reddev);
+        double variance = std::max((sqsum / nz) - (mean * mean), 0.0);
+        double stddev = std::sqrt(variance);
+        *stddev_val = stddev;
+    }
+    return CV_HAL_ERROR_OK;
+}
+
+inline int meanStdDev_8UC4(const uchar* src_data, size_t src_step, int width, int height,
+                             double* mean_val, double* stddev_val, uchar* mask, size_t mask_step) {
+    int nz = 0;
+    int vlmax = __riscv_vsetvlmax_e64m8();
+    vuint64m8_t vec_sum = __riscv_vmv_v_x_u64m8(0, vlmax);
+    vuint64m8_t vec_sqsum = __riscv_vmv_v_x_u64m8(0, vlmax);
+    if (mask) {
+        for (int i = 0; i < height; ++i) {
+            const uchar* src_row = src_data + i * src_step;
+            const uchar* mask_row = mask + i * mask_step;
+            int j = 0, jm = 0, vl, vlm;
+            for ( ; j < width*4; j += vl, jm += vlm) {
+                vl = __riscv_vsetvl_e8m1(width*4 - j);
+                vlm = __riscv_vsetvl_e8mf4(width - jm);
+                auto vec_pixel_u8 = __riscv_vle8_v_u8m1(src_row + j, vl);
+                auto vmask_u8mf4 = __riscv_vle8_v_u8mf4(mask_row + jm, vlm);
+                auto vmask_u32 = __riscv_vzext_vf4(vmask_u8mf4, vlm);
+                // 0 -> 0000; 1 -> 1111
+                vmask_u32 = __riscv_vmul(vmask_u32, 0b00000001000000010000000100000001, vlm);
+                auto vmask_u8 = __riscv_vreinterpret_u8m1(vmask_u32);
+                auto vec_pixel = __riscv_vzext_vf4(vec_pixel_u8, vl);
+                auto vmask = __riscv_vmseq_vx_u8m1_b8(vmask_u8, 1, vl);
+                vec_sum = __riscv_vwaddu_wv_u64m8_tumu(vmask, vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vwmaccu_vv_u64m8_tumu(vmask, vec_sqsum, vec_pixel, vec_pixel, vl);
+                nz += __riscv_vcpop_m_b8(vmask, vl);
+            }
+            nz /= 4;
+        }
+    } else {
+        for (int i = 0; i < height; i++) {
+            const uchar*  src_row = src_data + i * src_step;
+            int j = 0, vl;
+            for ( ; j <  width*4; j += vl) {
+                vl = __riscv_vsetvl_e8m1(width*4 - j);
+                auto vec_pixel_u8 = __riscv_vle8_v_u8m1(src_row + j, vl);
+                auto vec_pixel = __riscv_vzext_vf4(vec_pixel_u8, vl);
+                vec_sum = __riscv_vwaddu_wv_u64m8_tu(vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vwmaccu_vv_u64m8_tu(vec_sqsum, vec_pixel, vec_pixel, vl);
+            }
+        }
+        nz = height * width;
+    }
+    if (nz == 0) {
+        if (mean_val) *mean_val = 0.0;
+        if (stddev_val) *stddev_val = 0.0;
+        return CV_HAL_ERROR_OK;
+    }
+    uint64_t s[256], sq[256], sum[4] = {0}, sqsum[4] = {0};
+    __riscv_vse64(s, vec_sum, vlmax);
+    __riscv_vse64(sq, vec_sqsum, vlmax);
+    for (int i = 0; i < vlmax; ++i)
+    {
+        sum[i % 4] += s[i];
+        sqsum[i % 4] += sq[i];
+    }
+    if (mean_val) {
+        mean_val[0] = (double)sum[0] / nz;
+        mean_val[1] = (double)sum[1] / nz;
+        mean_val[2] = (double)sum[2] / nz;
+        mean_val[3] = (double)sum[3] / nz;
+    }
+    if (stddev_val) {
+        stddev_val[0] = std::sqrt(std::max(((double)sqsum[0] / nz) - (mean_val[0] * mean_val[0]), 0.0));
+        stddev_val[1] = std::sqrt(std::max(((double)sqsum[1] / nz) - (mean_val[1] * mean_val[1]), 0.0));
+        stddev_val[2] = std::sqrt(std::max(((double)sqsum[2] / nz) - (mean_val[2] * mean_val[2]), 0.0));
+        stddev_val[3] = std::sqrt(std::max(((double)sqsum[3] / nz) - (mean_val[3] * mean_val[3]), 0.0));
+    }
+    return CV_HAL_ERROR_OK;
+}
+
+inline int meanStdDev_32FC1(const uchar* src_data, size_t src_step, int width, int height,
+                             double* mean_val, double* stddev_val, uchar* mask, size_t mask_step) {
+    int nz = 0;
+    int vlmax = __riscv_vsetvlmax_e64m4();
+    vfloat64m4_t vec_sum = __riscv_vfmv_v_f_f64m4(0, vlmax);
+    vfloat64m4_t vec_sqsum = __riscv_vfmv_v_f_f64m4(0, vlmax);
+    src_step /= sizeof(float);
+    if (mask) {
+        for (int i = 0; i < height; ++i) {
+            const float* src_row0 = reinterpret_cast<const float*>(src_data) + i * src_step;
+            const uchar* mask_row = mask + i * mask_step;
+            int j = 0, vl;
+            for ( ; j < width; j += vl) {
+                vl = __riscv_vsetvl_e32m2(width - j);
+                auto vec_pixel = __riscv_vle32_v_f32m2(src_row0 + j, vl);
+                auto vmask_u8 = __riscv_vle8_v_u8mf2(mask_row + j, vl);
+                auto vmask_u32 = __riscv_vzext_vf4(vmask_u8, vl);
+                auto vmask = __riscv_vmseq_vx_u32m2_b16(vmask_u32, 1, vl);
+                vec_sum = __riscv_vfwadd_wv_f64m4_tumu(vmask, vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vfwmacc_vv_f64m4_tumu(vmask, vec_sqsum, vec_pixel, vec_pixel, vl);
+                nz += __riscv_vcpop_m_b16(vmask, vl);
+            }
+        }
+    } else {
+        for (int i = 0; i < height; i++) {
+            const float* src_row0 = reinterpret_cast<const float*>(src_data) + i * src_step;
+            int j = 0, vl;
+            for ( ; j < width; j += vl) {
+                vl = __riscv_vsetvl_e32m2(width - j);
+                auto vec_pixel = __riscv_vle32_v_f32m2(src_row0 + j, vl);
+                vec_sum = __riscv_vfwadd_wv_f64m4_tu(vec_sum, vec_sum, vec_pixel, vl);
+                vec_sqsum = __riscv_vfwmacc_vv_f64m4_tu(vec_sqsum, vec_pixel, vec_pixel, vl);
+            }
+        }
+        nz = height * width;
+    }
+    if (nz == 0) {
+        if (mean_val) *mean_val = 0.0;
+        if (stddev_val) *stddev_val = 0.0;
+        return CV_HAL_ERROR_OK;
+    }
+    auto zero = __riscv_vfmv_v_f_f64m1(0, vlmax);
+    auto vec_red = __riscv_vfmv_v_f_f64m1(0, vlmax);
+    auto vec_reddev = __riscv_vfmv_v_f_f64m1(0, vlmax);
+    vec_red = __riscv_vfredusum(vec_sum, zero, vlmax);
+    vec_reddev = __riscv_vfredusum(vec_sqsum, zero, vlmax);
+    double sum = __riscv_vfmv_f(vec_red);
+    double mean = sum / nz;
+    if (mean_val) {
+        *mean_val = mean;
+    }
+    if (stddev_val) {
+        double sqsum = __riscv_vfmv_f(vec_reddev);
+        double variance = std::max((sqsum / nz) - (mean * mean), 0.0);
+        double stddev = std::sqrt(variance);
+        *stddev_val = stddev;
+    }
+    return CV_HAL_ERROR_OK;
+}
+
+}}
+
+#endif