x86: optimize CumulativeSum with SIMD Kogge-Stone prefix scan

src/layer/x86/cumulativesum_x86.cpp

@@ -0,0 +1,108 @@
+// Copyright 2026 Tencent
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "cumulativesum_x86.h"
+
+#include "x86_usability.h"
+
+#include "cpu.h"
+
+namespace ncnn {
+
+#include "cumulativesum_x86_helper.h"
+
+CumulativeSum_x86::CumulativeSum_x86()
+{
+}
+
+int CumulativeSum_x86::forward_inplace(Mat& bottom_top_blob, const Option& opt) const
+{
+    const int dims = bottom_top_blob.dims;
+    const int positive_axis = axis < 0 ? dims + axis : axis;
+
+    if (dims == 1)
+    {
+        cumulative_sum_prefix_sum_row(bottom_top_blob, bottom_top_blob.w);
+        return 0;
+    }
+
+    if (dims == 2 && positive_axis == 0)
+    {
+        const int w = bottom_top_blob.w;
+        const int h = bottom_top_blob.h;
+        for (int i = 1; i < h; i++)
+        {
+            const float* prev_row = bottom_top_blob.row(i - 1);
+            float* this_row = bottom_top_blob.row(i);
+            cumulative_sum_add(prev_row, this_row, w);
+        }
+        return 0;
+    }
+
+    if (dims == 2 && positive_axis == 1)
+    {
+        const int w = bottom_top_blob.w;
+        const int h = bottom_top_blob.h;
+        #pragma omp parallel for num_threads(opt.num_threads)
+        for (int i = 0; i < h; i++)
+        {
+            cumulative_sum_prefix_sum_row(bottom_top_blob.row(i), w);
+        }
+        return 0;
+    }
+
+    if (dims == 3 && positive_axis == 0)
+    {
+        const int w = bottom_top_blob.w;
+        const int h = bottom_top_blob.h;
+        const int c = bottom_top_blob.c;
+        const int size = w * h;
+
+        for (int q = 1; q < c; q++)
+        {
+            const float* prev = bottom_top_blob.channel(q - 1);
+            float* cur = bottom_top_blob.channel(q);
+            cumulative_sum_add(prev, cur, size);
+        }
+        return 0;
+    }
+
+    if (dims == 3 && positive_axis == 1)
+    {
+        const int w = bottom_top_blob.w;
+        const int h = bottom_top_blob.h;
+        const int c = bottom_top_blob.c;
+
+        #pragma omp parallel for num_threads(opt.num_threads)
+        for (int q = 0; q < c; q++)
+        {
+            Mat this_channel = bottom_top_blob.channel(q);
+            for (int i = 1; i < h; i++)
+            {
+                const float* prev_row = this_channel.row(i - 1);
+                float* this_row = this_channel.row(i);
+                cumulative_sum_add(prev_row, this_row, w);
+            }
+        }
+        return 0;
+    }
+
+    if (dims == 3 && positive_axis == 2)
+    {
+        const int w = bottom_top_blob.w;
+        const int h = bottom_top_blob.h;
+        const int c = bottom_top_blob.c;
+        #pragma omp parallel for num_threads(opt.num_threads)
+        for (int idx = 0; idx < c * h; idx++)
+        {
+            const int q = idx / h;
+            const int i = idx - q * h;
+            cumulative_sum_prefix_sum_row(bottom_top_blob.channel(q).row(i), w);
+        }
+        return 0;
+    }
+
+    return -100;
+}
+
+} // namespace ncnn

src/layer/x86/cumulativesum_x86.h

@@ -0,0 +1,21 @@
+// Copyright 2026 Tencent
+// SPDX-License-Identifier: BSD-3-Clause
+
+#ifndef LAYER_CUMULATIVESUM_X86_H
+#define LAYER_CUMULATIVESUM_X86_H
+
+#include "cumulativesum.h"
+
+namespace ncnn {
+
+class CumulativeSum_x86 : public CumulativeSum
+{
+public:
+    CumulativeSum_x86();
+
+    virtual int forward_inplace(Mat& bottom_top_blob, const Option& opt) const;
+};
+
+} // namespace ncnn
+
+#endif // LAYER_CUMULATIVESUM_X86_H

src/layer/x86/cumulativesum_x86_avx2.cpp

@@ -0,0 +1,22 @@
+// Copyright 2026 Tencent
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include "cpu.h"
+#include "mat.h"
+#include "x86_usability.h"
+
+namespace ncnn {
+
+#include "cumulativesum_x86_helper.h"
+
+void cumulative_sum_prefix_sum_row_avx2(float* ptr, int w)
+{
+    cumulative_sum_prefix_sum_row_avx2_impl(ptr, w);
+}
+
+void cumulative_sum_add_avx2(const float* ptr, float* outptr, int size)
+{
+    cumulative_sum_add_avx2_impl(ptr, outptr, size);
+}
+
+} // namespace ncnn

src/layer/x86/cumulativesum_x86_helper.h

@@ -0,0 +1,149 @@
+// Copyright 2026 Tencent
+// SPDX-License-Identifier: BSD-3-Clause
+
+#if NCNN_RUNTIME_CPU && NCNN_AVX2 && __AVX__ && !__AVX2__
+void cumulative_sum_prefix_sum_row_avx2(float* ptr, int w);
+void cumulative_sum_add_avx2(const float* ptr, float* outptr, int size);
+#endif
+
+#if __SSE2__
+static inline __m128 cumulative_sum_prefix_sum4_ps(__m128 v)
+{
+    __m128 t = _mm_castsi128_ps(_mm_slli_si128(_mm_castps_si128(v), 4));
+    v = _mm_add_ps(v, t);
+    t = _mm_castsi128_ps(_mm_slli_si128(_mm_castps_si128(v), 8));
+    v = _mm_add_ps(v, t);
+    return v;
+}
+#endif
+
+#if __AVX2__
+static void cumulative_sum_prefix_sum_row_avx2_impl(float* ptr, int w)
+{
+    int j = 0;
+    float sum = 0.f;
+
+    __m256 base = _mm256_setzero_ps();
+    for (; j + 8 <= w; j += 8)
+    {
+        __m256 v = _mm256_loadu_ps(ptr + j);
+        __m256 t = _mm256_castsi256_ps(_mm256_slli_si256(_mm256_castps_si256(v), 4));
+        v = _mm256_add_ps(v, t);
+        t = _mm256_castsi256_ps(_mm256_slli_si256(_mm256_castps_si256(v), 8));
+        v = _mm256_add_ps(v, t);
+        __m256 lo = _mm256_permute2f128_ps(v, v, 0x08);
+        lo = _mm256_shuffle_ps(lo, lo, _MM_SHUFFLE(3, 3, 3, 3));
+        v = _mm256_add_ps(v, lo);
+        v = _mm256_add_ps(v, base);
+        _mm256_storeu_ps(ptr + j, v);
+        __m256 last = _mm256_permute2f128_ps(v, v, 0x11);
+        base = _mm256_shuffle_ps(last, last, _MM_SHUFFLE(3, 3, 3, 3));
+    }
+    if (j > 0)
+        sum = ptr[j - 1];
+
+    for (; j < w; j++)
+    {
+        sum += ptr[j];
+        ptr[j] = sum;
+    }
+}
+
+static void cumulative_sum_add_avx2_impl(const float* ptr, float* outptr, int size)
+{
+    int i = 0;
+
+    for (; i + 7 < size; i += 8)
+    {
+        __m256 _p = _mm256_loadu_ps(ptr + i);
+        __m256 _outp = _mm256_loadu_ps(outptr + i);
+        _outp = _mm256_add_ps(_outp, _p);
+        _mm256_storeu_ps(outptr + i, _outp);
+    }
+
+    for (; i < size; i++)
+    {
+        outptr[i] += ptr[i];
+    }
+}
+#endif // __AVX2__
+
+static void cumulative_sum_prefix_sum_row(float* ptr, int w)
+{
+#if NCNN_RUNTIME_CPU && NCNN_AVX2 && __AVX__ && !__AVX2__
+    if (ncnn::cpu_support_x86_avx2())
+    {
+        cumulative_sum_prefix_sum_row_avx2(ptr, w);
+        return;
+    }
+#endif
+
+    int j = 0;
+    float sum = 0.f;
+
+#if __AVX__
+    for (; j + 8 <= w; j += 8)
+    {
+        __m256 v = _mm256_loadu_ps(ptr + j);
+        __m128 v0 = cumulative_sum_prefix_sum4_ps(_mm256_castps256_ps128(v));
+        __m128 v1 = cumulative_sum_prefix_sum4_ps(_mm256_extractf128_ps(v, 1));
+        v1 = _mm_add_ps(v1, _mm_shuffle_ps(v0, v0, _MM_SHUFFLE(3, 3, 3, 3)));
+
+        __m256 out = _mm256_castps128_ps256(v0);
+        out = _mm256_insertf128_ps(out, v1, 1);
+        out = _mm256_add_ps(out, _mm256_set1_ps(sum));
+        _mm256_storeu_ps(ptr + j, out);
+        sum = ptr[j + 7];
+    }
+#elif __SSE2__
+    for (; j + 4 <= w; j += 4)
+    {
+        __m128 v = cumulative_sum_prefix_sum4_ps(_mm_loadu_ps(ptr + j));
+        v = _mm_add_ps(v, _mm_set1_ps(sum));
+        _mm_storeu_ps(ptr + j, v);
+        sum = ptr[j + 3];
+    }
+#endif
+
+    for (; j < w; j++)
+    {
+        sum += ptr[j];
+        ptr[j] = sum;
+    }
+}
+
+static void cumulative_sum_add(const float* ptr, float* outptr, int size)
+{
+#if NCNN_RUNTIME_CPU && NCNN_AVX2 && __AVX__ && !__AVX2__
+    if (ncnn::cpu_support_x86_avx2())
+    {
+        cumulative_sum_add_avx2(ptr, outptr, size);
+        return;
+    }
+#endif
+
+    int i = 0;
+
+#if __AVX__
+    for (; i + 7 < size; i += 8)
+    {
+        __m256 _p = _mm256_loadu_ps(ptr + i);
+        __m256 _outp = _mm256_loadu_ps(outptr + i);
+        _outp = _mm256_add_ps(_outp, _p);
+        _mm256_storeu_ps(outptr + i, _outp);
+    }
+#elif __SSE2__
+    for (; i + 3 < size; i += 4)
+    {
+        __m128 _p = _mm_loadu_ps(ptr + i);
+        __m128 _outp = _mm_loadu_ps(outptr + i);
+        _outp = _mm_add_ps(_outp, _p);
+        _mm_storeu_ps(outptr + i, _outp);
+    }
+#endif
+
+    for (; i < size; i++)
+    {
+        outptr[i] += ptr[i];
+    }
+}

tests/test_cumulativesum.cpp

@@ -49,12 +49,40 @@ static int test_cumulativesum_3d()
            || test_cumulativesum(RandomMat(303, 200, 103), -2);
 }
 
+static int test_cumulativesum_boundary()
+{
+    return 0
+           || test_cumulativesum(RandomMat(1), 0)
+           || test_cumulativesum(RandomMat(2), 0)
+           || test_cumulativesum(RandomMat(3), 0)
+           || test_cumulativesum(RandomMat(4), 0)
+           || test_cumulativesum(RandomMat(5), 0)
+           || test_cumulativesum(RandomMat(7), 0)
+           || test_cumulativesum(RandomMat(8), 0)
+           || test_cumulativesum(RandomMat(9), 0)
+           || test_cumulativesum(RandomMat(15), 0)
+           || test_cumulativesum(RandomMat(16), 0)
+           || test_cumulativesum(RandomMat(17), 0)
+           || test_cumulativesum(RandomMat(32), 0)
+           || test_cumulativesum(RandomMat(8, 5), 1)
+           || test_cumulativesum(RandomMat(16, 5), 1)
+           || test_cumulativesum(RandomMat(17, 5), 1)
+           || test_cumulativesum(RandomMat(1, 5), 1)
+           || test_cumulativesum(RandomMat(3, 5), 1)
+           || test_cumulativesum(RandomMat(8, 5, 3), 2)
+           || test_cumulativesum(RandomMat(16, 5, 3), 2)
+           || test_cumulativesum(RandomMat(17, 5, 3), 2)
+           || test_cumulativesum(RandomMat(1, 5, 3), 2)
+           || test_cumulativesum(RandomMat(3, 5, 3), 2);
+}
+
 int main()
 {
     SRAND(7767517);
 
     return 0
            || test_cumulativesum_1d()
            || test_cumulativesum_2d()
-           || test_cumulativesum_3d();
+           || test_cumulativesum_3d()
+           || test_cumulativesum_boundary();
 }