bitrev.c

#include <stdio.h>
#include <inttypes.h>

uint32_t rev(uint32_t x)
{
     x = (x & 0x55555555) << 1 | (x >> 1) & 0x55555555;
     x = (x & 0x33333333) << 2 | (x >> 2) & 0x33333333;
     x = (x & 0x0F0F0F0F) << 4 | (x >> 4) & 0x0F0F0F0F;
     x = (x << 24) | ((x & 0xFF00) << 8) |
	  (x >> 8) & 0xFF00 | (x >> 24);
     return x;
}

int main(int argc, char *argv[])
{
     uint32_t i = atoi(argv[1]);
     printf("%ld", rev(i));
     return 0;
}