代码

#include<bits/stdc++.h>
unsigned b[50000000], c0[256], c1[256], c2[256], c3[256];
unsigned *pos[256];

#define gao(cnt,op)					\
  int sum=-1;						\
  for (i=0;i<256;++i) pos[i]=B+sum, sum+=cnt[i];	\
  for (i=0;i<n;i+=4){					\
    *(++pos[A[i] op])=A[i];				\
    *(++pos[A[i+1] op])=A[i+1];				\
    *(++pos[A[i+2] op])=A[i+2];				\
    *(++pos[A[i+3] op])=A[i+3];				\
  }							\
  T=A; A=B; B=T;

void sort(unsigned *a,int n){
  {
    register unsigned i;
    for (i=0;i<n;++i){
      ++c0[a[i]&255];
      ++c1[a[i]>>8&255];
      ++c2[a[i]>>16&255];
      ++c3[a[i]>>24&255];
    }
  }
    
  unsigned *A=a, *B=b, *T;
    
  {
    register unsigned i;
    gao(c0,&255);
  }
  {
    register unsigned i;
    gao(c1,>>8&255);
  }
  {
    register unsigned i;
    gao(c2,>>16&255);
  }
  {
    register unsigned i;
    gao(c3,>>24&255);
  }
}

评测结果