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| 1 | +{ |
| 2 | + "cells": [ |
| 3 | + { |
| 4 | + "cell_type": "code", |
| 5 | + "execution_count": null, |
| 6 | + "id": "2efd7be2-5ea7-42cb-a2e2-9ddb409bc893", |
| 7 | + "metadata": {}, |
| 8 | + "outputs": [], |
| 9 | + "source": [ |
| 10 | + "#include <cstddef>\n", |
| 11 | + "#include <vector>\n", |
| 12 | + "#include <random>\n", |
| 13 | + "#include <iostream>\n", |
| 14 | + "\n", |
| 15 | + "#include <xsimd/xsimd.hpp>" |
| 16 | + ] |
| 17 | + }, |
| 18 | + { |
| 19 | + "cell_type": "markdown", |
| 20 | + "id": "6f498bff-4366-4e1c-ab25-3d3589740e78", |
| 21 | + "metadata": {}, |
| 22 | + "source": [ |
| 23 | + "Comparing two implementation of element wise mean." |
| 24 | + ] |
| 25 | + }, |
| 26 | + { |
| 27 | + "cell_type": "code", |
| 28 | + "execution_count": null, |
| 29 | + "id": "cf6b2c85-1427-49a3-8bef-0340601319e8", |
| 30 | + "metadata": {}, |
| 31 | + "outputs": [], |
| 32 | + "source": [ |
| 33 | + "std::vector<double> random_vector(std::size_t n)\n", |
| 34 | + "{\n", |
| 35 | + " static std::mt19937 gen(42);\n", |
| 36 | + " std::uniform_real_distribution<double> dist(0.0, 1.0);\n", |
| 37 | + " std::vector<double> v(n);\n", |
| 38 | + " for (auto& x : v)\n", |
| 39 | + " {\n", |
| 40 | + " x = dist(gen);\n", |
| 41 | + " }\n", |
| 42 | + " return v;\n", |
| 43 | + "}" |
| 44 | + ] |
| 45 | + }, |
| 46 | + { |
| 47 | + "cell_type": "code", |
| 48 | + "execution_count": null, |
| 49 | + "id": "a2ab6177-60e2-4d65-b323-51a6a21ad530", |
| 50 | + "metadata": {}, |
| 51 | + "outputs": [], |
| 52 | + "source": [ |
| 53 | + "std::vector<double> mean_scalar(const std::vector<double>& a, const std::vector<double>& b)\n", |
| 54 | + "{\n", |
| 55 | + " std::size_t size = a.size();\n", |
| 56 | + " std::vector<double> res(size);\n", |
| 57 | + " for (std::size_t i = 0; i < size; ++i)\n", |
| 58 | + " {\n", |
| 59 | + " res[i] = (a[i] + b[i]) / 2;\n", |
| 60 | + " }\n", |
| 61 | + " return res;\n", |
| 62 | + "}" |
| 63 | + ] |
| 64 | + }, |
| 65 | + { |
| 66 | + "cell_type": "code", |
| 67 | + "execution_count": null, |
| 68 | + "id": "082ed2cd-273a-4c3c-a206-03b1efe49482", |
| 69 | + "metadata": {}, |
| 70 | + "outputs": [], |
| 71 | + "source": [ |
| 72 | + "std::vector<double> mean_simd(const std::vector<double>& a, const std::vector<double>& b)\n", |
| 73 | + "{\n", |
| 74 | + " using b_type = xsimd::batch<double>;\n", |
| 75 | + " std::size_t inc = b_type::size;\n", |
| 76 | + " std::size_t size = a.size();\n", |
| 77 | + " std::vector<double> res(size);\n", |
| 78 | + "\n", |
| 79 | + " // size for which the vectorization is possible\n", |
| 80 | + " std::size_t vec_size = size - size % inc;\n", |
| 81 | + " for (std::size_t i = 0; i < vec_size; i += inc)\n", |
| 82 | + " {\n", |
| 83 | + " b_type avec = b_type::load_unaligned(&a[i]);\n", |
| 84 | + " b_type bvec = b_type::load_unaligned(&b[i]);\n", |
| 85 | + " b_type rvec = (avec + bvec) / 2;\n", |
| 86 | + " rvec.store_unaligned(&res[i]);\n", |
| 87 | + " }\n", |
| 88 | + " // Remaining part that cannot be vectorize\n", |
| 89 | + " for (std::size_t i = vec_size; i < size; ++i)\n", |
| 90 | + " {\n", |
| 91 | + " res[i] = (a[i] + b[i]) / 2;\n", |
| 92 | + " }\n", |
| 93 | + " return res;\n", |
| 94 | + "}" |
| 95 | + ] |
| 96 | + }, |
| 97 | + { |
| 98 | + "cell_type": "code", |
| 99 | + "execution_count": null, |
| 100 | + "id": "5959864d", |
| 101 | + "metadata": {}, |
| 102 | + "outputs": [], |
| 103 | + "source": [ |
| 104 | + "// Print v[begin:end] as grayscale ASCII blocks (dark = 0, light = 1).\n", |
| 105 | + "void print_grayscale(const std::vector<double>& v, std::size_t begin, std::size_t end)\n", |
| 106 | + "{\n", |
| 107 | + " for (std::size_t i = begin; i < end; ++i)\n", |
| 108 | + " {\n", |
| 109 | + " // map value in [0, 1] to a 24-bit truecolor gray (256 levels)\n", |
| 110 | + " int gray = static_cast<int>(v[i] * 255);\n", |
| 111 | + " std::cout << \"\\033[38;2;\" << gray << \";\" << gray << \";\" << gray << \"m█\";\n", |
| 112 | + " }\n", |
| 113 | + " std::cout << \"\\033[0m\\n\";\n", |
| 114 | + "}" |
| 115 | + ] |
| 116 | + }, |
| 117 | + { |
| 118 | + "cell_type": "code", |
| 119 | + "execution_count": null, |
| 120 | + "id": "2068e201", |
| 121 | + "metadata": {}, |
| 122 | + "outputs": [], |
| 123 | + "source": [ |
| 124 | + "std::size_t n = 1000;\n", |
| 125 | + "std::vector<double> const a = random_vector(n);\n", |
| 126 | + "std::vector<double> const b = random_vector(n);" |
| 127 | + ] |
| 128 | + }, |
| 129 | + { |
| 130 | + "cell_type": "code", |
| 131 | + "execution_count": null, |
| 132 | + "id": "9d5a7adc-5b55-4224-a4ca-5e438d1fc4d4", |
| 133 | + "metadata": {}, |
| 134 | + "outputs": [], |
| 135 | + "source": [ |
| 136 | + "auto const res_simd = mean_simd(a, b);" |
| 137 | + ] |
| 138 | + }, |
| 139 | + { |
| 140 | + "cell_type": "code", |
| 141 | + "execution_count": null, |
| 142 | + "id": "d279cd74-c397-4ea8-af15-3745f043f656", |
| 143 | + "metadata": {}, |
| 144 | + "outputs": [], |
| 145 | + "source": [ |
| 146 | + "auto const res_scalar = mean_scalar(a, b);" |
| 147 | + ] |
| 148 | + }, |
| 149 | + { |
| 150 | + "cell_type": "markdown", |
| 151 | + "id": "a04ae145", |
| 152 | + "metadata": {}, |
| 153 | + "source": [ |
| 154 | + "Each block is a value in `[0, 1]` shown as a grayscale shade (dark = low, light = high). The vector is drawn in chunks of 100, each chunk stacking input `a`, the SIMD mean, the scalar mean, and input `b`. The two mean rows should look identical, each sitting between its inputs." |
| 155 | + ] |
| 156 | + }, |
| 157 | + { |
| 158 | + "cell_type": "code", |
| 159 | + "execution_count": null, |
| 160 | + "id": "59ca84ad-8b97-4523-af0d-d3eca01b41d0", |
| 161 | + "metadata": {}, |
| 162 | + "outputs": [], |
| 163 | + "source": [ |
| 164 | + "std::size_t const width = 100;\n", |
| 165 | + "for (std::size_t begin = 0; begin < n; begin += width)\n", |
| 166 | + "{\n", |
| 167 | + " std::size_t end = std::min(begin + width, n);\n", |
| 168 | + " std::cout << \"a: \";\n", |
| 169 | + " print_grayscale(a, begin, end);\n", |
| 170 | + " std::cout << \"simd: \";\n", |
| 171 | + " print_grayscale(res_simd, begin, end);\n", |
| 172 | + " std::cout << \"scalar: \";\n", |
| 173 | + " print_grayscale(res_scalar, begin, end);\n", |
| 174 | + " std::cout << \"b: \";\n", |
| 175 | + " print_grayscale(b, begin, end);\n", |
| 176 | + " std::cout << \"\\n\";\n", |
| 177 | + "}" |
| 178 | + ] |
| 179 | + }, |
| 180 | + { |
| 181 | + "cell_type": "code", |
| 182 | + "execution_count": null, |
| 183 | + "id": "90b86fb4-0426-43fd-b5fc-8626ef8732a5", |
| 184 | + "metadata": {}, |
| 185 | + "outputs": [], |
| 186 | + "source": [] |
| 187 | + } |
| 188 | + ], |
| 189 | + "metadata": { |
| 190 | + "kernelspec": { |
| 191 | + "display_name": "C++17", |
| 192 | + "language": "cpp", |
| 193 | + "name": "xcpp17" |
| 194 | + }, |
| 195 | + "language_info": { |
| 196 | + "codemirror_mode": "text/x-c++src", |
| 197 | + "file_extension": ".cpp", |
| 198 | + "mimetype": "text/x-c++src", |
| 199 | + "name": "C++", |
| 200 | + "nbconvert_exporter": "", |
| 201 | + "pygments_lexer": "", |
| 202 | + "version": "cxx17" |
| 203 | + } |
| 204 | + }, |
| 205 | + "nbformat": 4, |
| 206 | + "nbformat_minor": 5 |
| 207 | +} |
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