代码

void sort(unsigned *a, int n)
{
    unsigned *b=new unsigned[n];
	unsigned *ptr0[256],*ptr8[256],*ptr16[256],*ptr24[256];
	unsigned cnt0[256], cnt8[256], cnt16[256], cnt24[256];
    unsigned *p;
    for (int i = 0; i < 256; ++i)
    {
        cnt0[i] = 0;
        cnt8[i] = 0;
        cnt16[i] = 0;
        cnt24[i] = 0;
    }
    for (int i = 0; i < n;)
    {
        ++cnt0[a[i] & 255], ++cnt8[a[i] >> 8 & 255], ++cnt16[a[i] >> 16 & 255], ++cnt24[a[i] >> 24], ++i;
        ++cnt0[a[i] & 255], ++cnt8[a[i] >> 8 & 255], ++cnt16[a[i] >> 16 & 255], ++cnt24[a[i] >> 24], ++i;
        ++cnt0[a[i] & 255], ++cnt8[a[i] >> 8 & 255], ++cnt16[a[i] >> 16 & 255], ++cnt24[a[i] >> 24], ++i;
        ++cnt0[a[i] & 255], ++cnt8[a[i] >> 8 & 255], ++cnt16[a[i] >> 16 & 255], ++cnt24[a[i] >> 24], ++i;
    }
    ptr0[0]=b-1,ptr8[0]=a-1,ptr16[0]=b-1,ptr24[0]=a-1;
    for (int i = 1; i < 256; ++i){
        ptr0[i] = ptr0[i-1]+cnt0[i-1];
		ptr8[i] = ptr8[i-1]+cnt8[i-1];
		ptr16[i] = ptr16[i-1]+cnt16[i-1];
		ptr24[i] = ptr24[i-1]+cnt24[i-1];
	}
#define countingSort(a,k) \
for (int i = 0; i < n; i += 4){\
    *++ptr##k[a[0]>>k&255]=a[0];\
    *++ptr##k[a[1]>>k&255]=a[1];\
    *++ptr##k[a[2]>>k&255]=a[2];\
    *++ptr##k[a[3]>>k&255]=a[3];\
}

	countingSort(a,0);
	countingSort(b,8);
	countingSort(a,16);
	countingSort(b,24);
	delete[] b;
}

评测结果