Question

I have a question as described: how to perform rotate shift in C without embedded assembly. To be more concrete, how to rotate shift a 32-bit int.

I’m now solving this problem with the help of type long long int, but I think it a little bit ugly and wanna know whether there is a more elegant method.

Kind regards.

Answer 1

(warning to future readers): Wikipedia’s code produces sub-optimal asm (gcc includes a branch or cmov). See Best practices for circular shift (rotate) operations in C++ for efficient UB-free rotates.

---

From Wikipedia:

unsigned int _rotl(unsigned int value, int shift) {
    if ((shift &= 31) == 0)
      return value;
    return (value << shift) | (value >> (32 - shift));
}

unsigned int _rotr(unsigned int value, int shift) {
    if ((shift &= 31) == 0)
      return value;
    return (value >> shift) | (value << (32 - shift));
}