|
|
而其計(jì)算字符串hash值的方法如下，將源碼摘出來(lái)以供查備：
復(fù)制代碼 代碼如下:
static inline ulong zend_inline_hash_func(const char *arKey, uint nKeyLength)
{
register ulong hash = 5381; //此處初始值的設(shè)置有什么玄機(jī)么？
/* variant with the hash unrolled eight times */
for (; nKeyLength >= 8; nKeyLength -= 8) { //這種step=8的方式是為何？
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... */ //此處是將剩余的字符hash
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
}
ps：對(duì)于以下函數(shù)，仍有兩點(diǎn)不明：
hash = 5381設(shè)置的理由？
這種step=8的循環(huán)方式是為了效率么？
php技術(shù)：PHP中用hash實(shí)現(xiàn)的數(shù)組，轉(zhuǎn)載需保留來(lái)源！
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