开扒php内核函数,第二篇 hex2bin
我们还是从分析开始吧 先看这个函数的介绍吧 string hex2bin ( string $data ) 如果输入的十六进制字符串是奇数长数或者无效的十六进制字符串将会抛出 E_WARNING 级别的错误。 先看个例子 ?php $hex = hex2bin(6578616d706c65206865782064617461); var_dump(
我们还是从分析开始吧
先看这个函数的介绍吧
string hex2bin ( string $data
)
如果输入的十六进制字符串是奇数长数或者无效的十六进制字符串将会抛出 E_WARNING
级别的错误。
先看个例子
$hex = hex2bin("6578616d706c65206865782064617461");
var_dump($hex);
?>
以上例程的输出类似于:
string(16) "example hex data"
大家应该明白了吧
1,循环整个字符串
2,每两个16进制组成一个ascii字符 例如 65=》 0x6
3 ,输出结果
我是这样想的
因为上面要判断输入的字符串是否有效,所以加了一些判断,字符范围啊
还有一个关键点就是 为什么要减去 0 和87呢,因为要把16进制的字符转换为真实的数字,所以要减
但是上面的程序写得是有问题的,我是觉得可以优化的
看看php内核是怎样写的
我们可以看到,
1,作者没有使用high和low的两个变量,而是用str[i]代替去累加 注意作者是先移位,然后再加,我写的程序是一步到位,这也是一种技巧啊
2,还有一个地方就是j+=2,作者是用了两个j++去替代
3,加法用或运算去代替,比我们的快啊,什么情况可以用或运算呢,就是原始数的低位都是0,加上一个任何数,可以认为两个数进行异运算啦 例如 0xf0 | 0x0f = 0xff = 0xf0+0x0f 啦

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