http://stackoverflow.com/questions/9144800/c-reverse-bits-in-unsigned-integer
Reversing the bits in a word is annoying and it's easier just to output them in reverse order. E.g.
void write_u32(uint32_t x)
{
int i;
for (i = 0; i < 32; ++i)
putchar((x & ((uint32_t) 1 << (31 - i)) ? '1' : '0');
}
Here's the typical solution to reversing the bit order:
uint32_t reverse(uint32_t x)
{
x = ((x >> 1) & 0x55555555u) | ((x & 0x55555555u) << 1);
x = ((x >> 2) & 0x33333333u) | ((x & 0x33333333u) << 2);
x = ((x >> 4) & 0x0f0f0f0fu) | ((x & 0x0f0f0f0fu) << 4);
x = ((x >> 8) & 0x00ff00ffu) | ((x & 0x00ff00ffu) << 8);
x = ((x >> 16) & 0xffffu) | ((x & 0xffffu) << 16);
return x;
}