代码

void sort(unsigned *a,int n)
{
	unsigned *b=new unsigned[n];
	unsigned cnt0[256],cnt8[256],cnt16[256],cnt24[256];
    unsigned *ptr0[256], *ptr8[256], *ptr16[256], *ptr24[256];

    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;++i){
		++cnt0[a[i]>>0&255];
		++cnt8[a[i]>>8&255];
		++cnt16[a[i]>>16&255];
		++cnt24[a[i]>>24&255];
	}
    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]=cnt0[i]+ptr0[i-1];
		ptr8[i]=cnt8[i]+ptr8[i-1];
		ptr16[i]=cnt16[i]+ptr16[i-1];
		ptr24[i]=cnt24[i]+ptr24[i-1];
	}

#define countingSort(a,b,k) \
for(int i=0;i<n;++i) *++ptr##k[a[i]>>k&255]=a[i];

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

评测结果