user: What would the C source look like for the assembly code provided here?

```asm
<write_timestamp>:
  endbr64
  sub    $0x68,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x58(%rsp)
  xor    %eax,%eax
  lea    0x10(%rsp),%rsi
  mov    %edi,0xc(%rsp)
  lea    0xc(%rsp),%rdi
  call   <gmtime_r@plt>
  mov    0x10(%rsp),%eax
  lea    0x30(%rsp),%rdi
  movb   $0x2d,0x34(%rsp)
  movb   $0x2d,0x37(%rsp)
  lea    0x76c(%rax),%edx
  movb   $0x54,0x3a(%rsp)
  movslq %edx,%rax
  mov    %edx,%ecx
  movb   $0x3a,0x3d(%rsp)
  imul   $0x66666667,%rax,%rax
  sar    $0x1f,%ecx
  movb   $0x3a,0x40(%rsp)
  sar    $0x22,%rax
  sub    %ecx,%eax
  lea    (%rax,%rax,4),%ecx
  add    %ecx,%ecx
  sub    %ecx,%edx
  mov    %eax,%ecx
  add    $0x30,%edx
  sar    $0x1f,%ecx
  mov    %dl,0x33(%rsp)
  movslq %eax,%rdx
  imul   $0x66666667,%rdx,%rdx
  sar    $0x22,%rdx
  sub    %ecx,%edx
  lea    (%rdx,%rdx,4),%ecx
  add    %ecx,%ecx
  sub    %ecx,%eax
  mov    %edx,%ecx
  add    $0x30,%eax
  sar    $0x1f,%ecx
  mov    %al,0x32(%rsp)
  movslq %edx,%rax
  imul   $0x66666667,%rax,%rax
  sar    $0x22,%rax
  sub    %ecx,%eax
  lea    (%rax,%rax,4),%ecx
  add    %ecx,%ecx
  sub    %ecx,%edx
  mov    %eax,%ecx
  add    $0x30,%edx
  sar    $0x1f,%ecx
  mov    %dl,0x31(%rsp)
  movslq %eax,%rdx
  imul   $0x66666667,%rdx,%rdx
  sar    $0x22,%rdx
  sub    %ecx,%edx
  lea    (%rdx,%rdx,4),%edx
  add    %edx,%edx
  sub    %edx,%eax
  add    $0x30,%eax
  mov    %al,0x30(%rsp)
  mov    0x14(%rsp),%eax
  add    $0x1,%eax
  movslq %eax,%rdx
  mov    %eax,%ecx
  imul   $0x66666667,%rdx,%rdx
  sar    $0x1f,%ecx
  sar    $0x22,%rdx
  sub    %ecx,%edx
  lea    0x30(%rdx),%ecx
  lea    (%rdx,%rdx,4),%edx
  add    %edx,%edx
  mov    %cl,0x35(%rsp)
  sub    %edx,%eax
  add    $0x30,%eax
  mov    %al,0x36(%rsp)
  movslq 0x18(%rsp),%rax
  mov    %rax,%rdx
  imul   $0x66666667,%rax,%rax
  mov    %edx,%ecx
  sar    $0x1f,%ecx
  sar    $0x22,%rax
  sub    %ecx,%eax
  lea    0x30(%rax),%ecx
  lea    (%rax,%rax,4),%eax
  add    %eax,%eax
  mov    %cl,0x38(%rsp)
  sub    %eax,%edx
  movslq 0x1c(%rsp),%rax
  add    $0x30,%edx
  mov    %dl,0x39(%rsp)
  mov    %rax,%rdx
  imul   $0x66666667,%rax,%rax
  mov    %edx,%ecx
  sar    $0x1f,%ecx
  sar    $0x22,%rax
  sub    %ecx,%eax
  lea    0x30(%rax),%ecx
  lea    (%rax,%rax,4),%eax
  add    %eax,%eax
  mov    %cl,0x3b(%rsp)
  sub    %eax,%edx
  movslq 0x20(%rsp),%rax
  add    $0x30,%edx
  mov    %dl,0x3c(%rsp)
  mov    %rax,%rdx
  imul   $0x66666667,%rax,%rax
  mov    %edx,%ecx
  sar    $0x1f,%ecx
  sar    $0x22,%rax
  sub    %ecx,%eax
  lea    0x30(%rax),%ecx
  lea    (%rax,%rax,4),%eax
  add    %eax,%eax
  mov    %cl,0x3e(%rsp)
  sub    %eax,%edx
  movslq 0x24(%rsp),%rax
  add    $0x30,%edx
  mov    %dl,0x3f(%rsp)
  mov    %rax,%rdx
  imul   $0xffffffff88888889,%rax,%rax
  mov    %edx,%ecx
  shr    $0x20,%rax
  add    %edx,%eax
  sar    $0x5,%eax
  sar    $0x1f,%ecx
  sub    %ecx,%eax
  imul   $0x3c,%eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  movslq %eax,%rdx
  mov    %eax,%ecx
  imul   $0x66666667,%rdx,%rdx
  sar    $0x1f,%ecx
  sar    $0x22,%rdx
  sub    %ecx,%edx
  lea    0x30(%rdx),%ecx
  lea    (%rdx,%rdx,4),%edx
  add    %edx,%edx
  mov    %cl,0x41(%rsp)
  sub    %edx,%eax
  add    $0x30,%eax
  mov    %al,0x42(%rsp)
  mov    $0x5a,%eax
  mov    %ax,0x43(%rsp)
  call   <write_str@plt>
  mov    0x58(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L3
  add    $0x68,%rsp
  ret
L3:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void write_timestamp(uint64_t v) {
  time_t vtime;
  struct tm tm;
  char s[30], *sp;
  int i;
  vtime = v;
  gmtime_r(&vtime, &tm);
  i = tm.tm_year + 1900;
  sp = s + 3;
  *sp-- = i % 10 + '0';
  i /= 10;
  *sp-- = i % 10 + '0';
  i /= 10;
  *sp-- = i % 10 + '0';
  i /= 10;
  *sp = i % 10 + '0';
  sp += 4;
  *sp++ = '-';
  i = tm.tm_mon + 1;
  *sp++ = i / 10 + '0';
  *sp++ = i % 10 + '0';
  *sp++ = '-';
  i = tm.tm_mday;
  *sp++ = i / 10 + '0';
  *sp++ = i % 10 + '0';
  *sp++ = 'T';
  i = tm.tm_hour;
  *sp++ = i / 10 + '0';
  *sp++ = i % 10 + '0';
  *sp++ = ':';
  i = tm.tm_min;
  *sp++ = i / 10 + '0';
  *sp++ = i % 10 + '0';
  *sp++ = ':';
  i = tm.tm_sec % 60;
  *sp++ = i / 10 + '0';
  *sp++ = i % 10 + '0';
  *sp++ = 'Z';
  *sp = 0;
  write_str(s);
}
```