funcunit/site/node_modules/clean-css/lib/colors/rgb-to-hex.js

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module.exports = function RGBToHex(data) {
  return {
    process: function() {
      return data.replace(/rgb\((\-?\d+),(\-?\d+),(\-?\d+)\)/g, function(match, red, green, blue) {
        red = Math.max(0, Math.min(~~red, 255));
        green = Math.max(0, Math.min(~~green, 255));
        blue = Math.max(0, Math.min(~~blue, 255));

        // Credit: Asen  http://jsbin.com/UPUmaGOc/2/edit?js,console
        return '#' + ('00000' + (red << 16 | green << 8 | blue).toString(16)).slice(-6);
      });
    }
  };
};