#include "csapp.h"

/* Read in all data from stdin and write it out in a reverse
   order --- using only system APIs, so no malloc() for fread()
   or fwrite() */
void* our_malloc(size_t size)
{
 return Mmap(NULL,size,
             PROT_READ|PROT_WRITE,MAP_PRIVATE+MAP_ANON,
             -1,0);
}

int main()
{
  size_t sz =1<<14;
  char* buffer=our_malloc(sz);
  size_t b_read;
  int offset = 0;

  while((b_read = Read(0,buffer+offset,sz-offset)) !=0) {     
    offset += b_read;
    if(offset == sz) {
      char* old_buffer = buffer;      
      size_t old_sz = sz;
      sz=sz*2;
      buffer=our_malloc(sz);
      memcpy(buffer,old_buffer,old_sz);
      Munmap(old_buffer, old_sz);
    }
   }

  {
    char *out;
    size_t done = 0, i;
          
    out = mmap(NULL,sz,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANON,-1,0);
    
    for (i = 0; i < sz; i++)
      out[sz-1-i] = buffer[i];
    
    while(done < sz) {
      done += Write(1, out+done, sz-done);
    }
  }    

  return 0;
}