{
  "cells": [
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "# Generating an OpenCL kernel by Textual Substitution"
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "The simplest approach to generating code is to simply substitute snippets of text into an existing code \"template\". This can be done using the C preprocessor, simple string-based search and replace, or other string-value interpolation functionality present in the language. The example below demonstrates the latter case:"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 1,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": [
        "kernel = r\"\"\"\n",
        "    __kernel void {name}({arguments})\n",
        "    {{\n",
        "      int lid = get_local_id(0);\n",
        "      int gsize = get_global_size(0);\n",
        "      int work_group_start = get_local_size(0)*get_group_id(0);\n",
        "      long i;\n",
        "\n",
        "      for (i = work_group_start + lid; i < n; i += gsize)\n",
        "      {{\n",
        "        {operation};\n",
        "      }}\n",
        "    }}\n",
        "\"\"\""
      ]
    },
    {
      "cell_type": "markdown",
      "metadata": {},
      "source": [
        "One slightly unfortunate fact that plays into using Python's `.format()` facility for this purpose is that opening and closing braces must be escaped by doubling them."
      ]
    },
    {
      "cell_type": "code",
      "execution_count": 2,
      "metadata": {
        "collapsed": false
      },
      "outputs": [
        {
          "name": "stdout",
          "output_type": "stream",
          "text": [
            "\n",
            "    __kernel void scale(float *y, float a, float *x)\n",
            "    {\n",
            "      int lid = get_local_id(0);\n",
            "      int gsize = get_global_size(0);\n",
            "      int work_group_start = get_local_size(0)*get_group_id(0);\n",
            "      long i;\n",
            "\n",
            "      for (i = work_group_start + lid; i < n; i += gsize)\n",
            "      {\n",
            "        y[i] = a*x[i];\n",
            "      }\n",
            "    }\n",
            "\n"
          ]
        }
      ],
      "source": [
        "print(kernel.format(\n",
        "    name=\"scale\",\n",
        "    arguments=\"float *y, float a, float *x\",\n",
        "    operation=\"y[i] = a*x[i]\"\n",
        "))"
      ]
    },
    {
      "cell_type": "code",
      "execution_count": null,
      "metadata": {
        "collapsed": false
      },
      "outputs": [],
      "source": []
    }
  ],
  "metadata": {},
  "nbformat": 4,
  "nbformat_minor": 0
}