[Get the next power of 2 of an unsigned integer] #c

next_pow_2.c

// Assuming 64-bit long
unsigned long np2(unsigned long x) {
  --x;
  x |= x >> 1;
  x |= x >> 2;
  x |= x >> 4;
  x |= x >> 8;
  x |= x >> 16;
  x |= x >> 32;
  ++x;
  return x;
}

// Assuming x86 architecture and a compiler with __builtins
uint64_t nextpow2_64(uint64_t x) {
  return x == 1 ? 1 : 1 << (64 - __builtin_clzl(x - 1));
}

// Assuming x86 architecture and a compiler with __builtins
uint32_t nextpow2_32(uint32_t x) {
  return x == 1 ? 1 : 1 << (32 - __builtin_clz(x - 1));
}