Different ways to get the parity flag in C

parity_flag.c

/*
 * As shown below, this code is not meant for getting the parity of a number;
 * rather, it checks the parity flag. The reason is that the parity flag only
 * represents whether the least significant byte has odd or even number of set
 * bits. So, it should not be used to check the parity of a number in practice
 * unless the number is one byte long.
 *
 * Having said that, an implementation-defined function by Clang and GCC for
 * parity computation, __builtin_parity(x), returns 0 if x has even set bits and
 * 1 if odd, which is the opposite of the parity flag. That is the reason why
 * the code below applies NOT to the return value of __builtin_parity.
 */

#include <stdint.h>

#if defined(__GNUC__) || defined(__clang__)

int
parity1(int64_t n) {
  return !__builtin_parity(n);
}

#endif

#if defined(__i386) || defined(_M_IX86)

int
parity2(int64_t n) {
  int tmp;

  asm("cmp $0, %[n]\n\t"
      "lahf\n\t"
      "and $1024, %[tmp]"
      : [tmp] "=r"(tmp)
      : [n] "r"(n));

  return tmp;
}

#if defined(__SSE4_2__) || defined(__AVX__) || defined(__POPCNT__)

int
parity3(int64_t n) {
  int64_t tmp;

  asm("popcntq %[n], %%rax\n\t"
      "andq $1, %[tmp]"
      : [tmp] "=r"(tmp)
      : [n] "r"(n));

  return !tmp;
}

#endif

#endif