PHP全概率运算函数(优化版) Webgame开发必备

<?php
$setting = array(
// 黑色概率
0 => 0.99,
// 白色概率
1 => 0.01,
);
// Requires the GD Library
header("Content-type: image/png");
$im = imagecreatetruecolor(256, 256) or die("Cannot Initialize new GD image stream");
$white = imagecolorallocate($im, 255, 255, 255);
$start = microtime(true);
for ($y=0; $y<256; $y++) {
for ($x=0; $x<256; $x++) {
if (random($setting) === 1) {
imagesetpixel($im, $x, $y, $white);
}
}
}
$time = microtime(true) - $start;
header("X-Exec-Time: ".$time);
imagepng($im);
imagedestroy($im);

/**
* 全概率计算
*
* @param array $p array(‘a‘=>0.5,‘b‘=>0.2,‘c‘=>0.4)
* @return string 返回上面数组的key
* @author Lukin <my@lukin.cn>
*/
function random($ps){
static $arr = array(); $key = md5(serialize($ps));
if (!isset($arr[$key])) {
$max = array_sum($ps);
foreach ($ps as $k=>$v) {
$v = $v / $max * 10000;
for ($i=0; $i<$v; $i++) $arr[$key][] = $k;
}
}
return $arr[$key][mt_rand(0,count($arr[$key])-1)];
}
?>