#include <stdio.h>
#include <fcntl.h>

#define BLOCK_SIZE 0x1000

unsigned char data[BLOCK_SIZE];
unsigned char out_data[BLOCK_SIZE];

#define SWAP_INT(x)   ((((unsigned int)x & 0xFF) << 24) |(((unsigned int)x & 0xFF00) << 8) |(((unsigned int)x & 0xFF0000) >> 8) | (((unsigned int)x & 0xFF000000) >> 24))

int main(int argc, char * argv[])
{
    FILE * input;
    FILE * output;
    size_t read_count;
    size_t write_count;
    unsigned long * walker;
    unsigned long * out_walker;
    /* uncomment this if compiling on cygwin */
#if 0
    if(-1 == setmode(fileno(stdin), O_BINARY)){
        perror("Cannot set stdin to binary mode");
        return -1;
    }
    if(-1 == setmode(fileno(stdout), O_BINARY)){
        perror("Cannot set stdout to binary mode");
        return -1;
    }
#endif
    do{
        read_count = fread(data, 1, BLOCK_SIZE, stdin);
        if((0 != (read_count & 3))&&(0 != read_count)){
            fprintf(stderr, "Input size must be divisible by 4!\n");
            return -1;
        }
        if(read_count != 0){
            walker = (unsigned long*)data;
            out_walker = (unsigned long*)out_data;
            while(walker != (unsigned long*)(&data[BLOCK_SIZE])) {
                *out_walker = SWAP_INT(*walker);
                out_walker++; walker++;
            }

            write_count = fwrite(out_data, 1, read_count, stdout);
            if(read_count != write_count){
                perror("Unable to write data");
                return -1;
            }
        }
    }while(BLOCK_SIZE == read_count);

    return 0;
}