位运算怎么对一个十进制数去除个位?

Question

位运算怎么对一个十进制数去除个位

// 输入 12312312412341
// 返回 1231231241234

// 输入 99999999321
// 返回 9999999932

Answer 1

https://stackoverflow.com/questions/5558492/divide-by-10-using-bit-shifts

// This is a fast approximation that's inexact for large inputs
int32_t div10(int32_t dividend)
{
    int64_t invDivisor = 0x1999999A;
    return (int32_t) ((invDivisor * dividend) >> 32);
}

Answer 2

楼上的的函数用 js 写不怎么写不出来，但 url 中

unsigned divu10(unsigned n) {
    unsigned q, r;
    q = (n >> 1) + (n >> 2);
    q = q + (q >> 4);
    q = q + (q >> 8);
    q = q + (q >> 16);
    q = q >> 3;
    r = n - (((q << 2) + q) << 1);
    return q + (r > 9);
}

用 python 实现，可以

def divu10(n):
    q = (n>>1)+(n>>2)
    q=q+(q>>4)
    q=q+(q>>8)
    q=q+(q>>16)
    q=q>>3
    r = (n- ((n-(q<<2)+1) <<1))
    return q + (r>9)
print(divu10(899))