// Example of dual value return in C using by-value structs.  Contrast
// twoatoi.S.
//
// Compiling with -Os gives assembly like this, showing that the
// struct is being returned in rax and edx:
// 
// 107c: e8 18 01 00 00        call 1199 <atoi_two>
// 1081: 48 39 c7              cmp rdi, rax
// 1084: 48 8d 3d 79 0f 00 00  lea rdi, [rip+0xf79]
// 108b: 89 d6                 mov esi, edx
// 108d: 49 0f 45 fc           cmovne rdi,r12
// 1091: 31 c0                 xor eax,eax
// 1093: e8 a8 ff ff ff        call 1040 <printf@plt>
//
// Without -Os it still uses the same calling convention, it’s just
// harder to understand.

#include <stdio.h>

typedef struct { const char *p; int val; } numconversion;

numconversion atoi_two(const char *s)
{
  int n = 0;
  while ('0' <= *s && *s <= '9') n = 10 * n + *s++ - '0';
  return (numconversion){ s, n };
}

int main(int argc, char **argv)
{
  while (--argc) {
    char *s = *++argv;
    numconversion n = atoi_two(s);
    printf(n.p == s ? "(fail) " : "%d ", n.val);
  }

  printf("\n");
  return 0;
}