user: Converte this assembly snippet into its equivalent C code:

```asm
<oo__strtimetosint64>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x30,%rsp
  mov    %rdi,-0x28(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  movq   $0x0,-0x18(%rbp)
  mov    -0x28(%rbp),%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%edx
  sub    %edx,%eax
  shl    $0x3,%eax
  mov    %eax,%ecx
  mov    -0x28(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    $0x64,%edx
  imul   %edx,%eax
  lea    (%rcx,%rax,1),%edx
  mov    -0x28(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%ecx
  mov    %ecx,%eax
  shl    $0x2,%eax
  add    %ecx,%eax
  add    %eax,%eax
  add    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  add    $0x64,%eax
  mov    %al,-0x20(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x5,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  add    %eax,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x6,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  sub    $0x31,%eax
  mov    %al,-0x1f(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x8,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  add    %eax,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x9,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  sub    $0x30,%eax
  mov    %al,-0x1e(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xb,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  add    %eax,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xc,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  sub    $0x30,%eax
  mov    %al,-0x1d(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0xe,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  add    %eax,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0xf,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  sub    $0x30,%eax
  mov    %al,-0x1c(%rbp)
  mov    -0x28(%rbp),%rax
  add    $0x11,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  sub    $0x30,%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  add    %eax,%eax
  mov    %eax,%edx
  mov    -0x28(%rbp),%rax
  add    $0x12,%rax
  movzbl (%rax),%eax
  add    %edx,%eax
  sub    $0x30,%eax
  mov    %al,-0x1b(%rbp)
  lea    -0x20(%rbp),%rax
  mov    %rax,%rdi
  call   <timegm@plt>
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L8
  call   <__stack_chk_fail@plt>
L8:
  leave
  ret
```

assistant: ```c
int64_t oo__strtimetosint64(const char *s) {
  struct tm tm;
  tm.tm_isdst = 0;
  tm.tm_year = (s[0] - '0') * 1000 + (s[1] - '0') * 100 + (s[2] - '0') * 10 + (s[3] - '0') - 1900;
  tm.tm_mon = (s[5] - '0') * 10 + s[6] - '0' - 1;
  tm.tm_mday = (s[8] - '0') * 10 + s[9] - '0';
  tm.tm_hour = (s[11] - '0') * 10 + s[12] - '0';
  tm.tm_min = (s[14] - '0') * 10 + s[15] - '0';
  tm.tm_sec = (s[17] - '0') * 10 + s[18] - '0';
  return timegm(&tm);
}
```