PHP全概率运算函数(优化版) Webgame开发必备

代码如下：

<?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 $p array('a'=>0.5,'b'=>0.2,'c'=>0.4) 
* @return string 返回上面数组的key 
* @author Lukin <[email protected]> 
*/ 
function random($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)]; 
} 
?>