php hash算法实现数组的方法
PHP中使用最多的非Array莫属了,那Array是如何实现的？在PHP内部Array通过一个hashtable来实现,其中使用链接法解决hash冲突的问题,这样最坏情况下,查找Array元素的复杂度为O(N),最好则为1.
static inline ulong zend_inline_hash_func( const char *arKey, uint nKeyLength) { register ulong hash = 5381; //此处初始值的设置有什么玄机么？ /* variant with the hash unrolled eight times */ for (; nKeyLength >= 8; nKeyLength -= 8) { //这种step=8的方式是为何？ hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; //比直接*33要快 hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; hash = ((hash << 5) + hash) + *arKey++; } switch (nKeyLength) { case 7: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ //此处是将剩余的字符hash //开源代码phpfensi测试数据 case 6: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ case 5: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ case 4: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ case 3: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ case 2: hash = ((hash << 5) + hash) + *arKey++; /* fallthrough... */ case 1: hash = ((hash << 5) + hash) + *arKey++; break ; case 0: break ; EMPTY_SWITCH_DEFAULT_CASE() } return hash; //返回hash值 }查看更多关于php hash算法实现数组的方法 - php高级应用的详细内容...
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