user: Please show me the C implementation that matches the assembly code listed below:

```asm
<iso8601wknum>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x40,%rsp
  mov    %rdi,-0x38(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  mov    -0x38(%rbp),%rax
  mov    $0x1,%esi
  mov    %rax,%rdi
  call   <weeknumber@plt>
  mov    %eax,-0x30(%rbp)
  mov    -0x38(%rbp),%rax
  mov    (%rax),%esi
  mov    -0x38(%rbp),%rax
  mov    0x4(%rax),%eax
  movslq %eax,%rdx
  imul   $0xffffffff92492493,%rdx,%rdx
  shr    $0x20,%rdx
  add    %eax,%edx
  sar    $0x2,%edx
  mov    %eax,%edi
  sar    $0x1f,%edi
  mov    %edx,%ecx
  sub    %edi,%ecx
  mov    %ecx,%edx
  shl    $0x3,%edx
  sub    %ecx,%edx
  sub    %edx,%eax
  mov    %eax,%ecx
  mov    %esi,%eax
  sub    %ecx,%eax
  mov    %eax,-0x2c(%rbp)
  cmpl   $0x0,-0x2c(%rbp)
  jns    L105
  addl   $0x7,-0x2c(%rbp)
L105:
  cmpl   $0x6,-0x2c(%rbp)
  jg     L15
  cmpl   $0x5,-0x2c(%rbp)
  jge    L209
  cmpl   $0x4,-0x2c(%rbp)
  jg     L15
  cmpl   $0x2,-0x2c(%rbp)
  jge    L55
  cmpl   $0x0,-0x2c(%rbp)
  je     L209
  cmpl   $0x1,-0x2c(%rbp)
  jmp    L15
L55:
  addl   $0x1,-0x30(%rbp)
  jmp    L15
L209:
  cmpl   $0x0,-0x30(%rbp)
  jne    L21
  mov    -0x38(%rbp),%rcx
  mov    (%rcx),%rax
  mov    0x8(%rcx),%rdx
  mov    %rax,-0x20(%rbp)
  mov    %rdx,-0x18(%rbp)
  mov    0x10(%rcx),%eax
  mov    %eax,-0x10(%rbp)
  mov    -0x10(%rbp),%eax
  sub    $0x1,%eax
  mov    %eax,-0x10(%rbp)
  movl   $0xb,-0x18(%rbp)
  movl   $0x1f,-0x14(%rbp)
  cmpl   $0x0,-0x2c(%rbp)
  je     L52
  mov    -0x2c(%rbp),%eax
  sub    $0x1,%eax
  jmp    L146
L52:
  mov    $0x6,%eax
L146:
  mov    %eax,-0x20(%rbp)
  mov    -0x10(%rbp),%eax
  add    $0x76c,%eax
  mov    %eax,%edi
  call   <isleap@plt>
  add    $0x16c,%eax
  mov    %eax,-0x1c(%rbp)
  lea    -0x20(%rbp),%rax
  mov    %rax,%rdi
  call   <iso8601wknum>
  mov    %eax,-0x30(%rbp)
L21:
  nop
L15:
  mov    -0x38(%rbp),%rax
  mov    0x8(%rax),%eax
  cmp    $0xb,%eax
  jne    L182
  mov    -0x38(%rbp),%rax
  mov    (%rax),%eax
  mov    %eax,-0x28(%rbp)
  mov    -0x38(%rbp),%rax
  mov    0xc(%rax),%eax
  mov    %eax,-0x24(%rbp)
  cmpl   $0x1,-0x28(%rbp)
  jne    L14
  cmpl   $0x1c,-0x24(%rbp)
  jle    L14
  cmpl   $0x1f,-0x24(%rbp)
  jle    L78
L14:
  cmpl   $0x2,-0x28(%rbp)
  jne    L63
  cmpl   $0x1e,-0x24(%rbp)
  je     L78
  cmpl   $0x1f,-0x24(%rbp)
  je     L78
L63:
  cmpl   $0x3,-0x28(%rbp)
  jne    L182
  cmpl   $0x1f,-0x24(%rbp)
  jne    L182
L78:
  movl   $0x1,-0x30(%rbp)
L182:
  mov    -0x30(%rbp),%eax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L86
  call   <__stack_chk_fail@plt>
L86:
  leave
  ret
```

assistant: ```c
int iso8601wknum(const struct tm *timeptr) {
  int weeknum, jan1day, diff;
  weeknum = weeknumber(timeptr, 1);
  jan1day = timeptr->tm_wday - (timeptr->tm_yday % 7);
  if (jan1day < 0)
    jan1day += 7;
  switch (jan1day) {
  case 1:
    break;
  case 2:
  case 3:
  case 4:
    weeknum++;
    break;
  case 5:
  case 6:
  case 0:
    if (weeknum == 0) {
      struct tm dec31ly;
      dec31ly = *timeptr;
      dec31ly.tm_year--;
      dec31ly.tm_mon = 11;
      dec31ly.tm_mday = 31;
      dec31ly.tm_wday = (jan1day == 0) ? 6 : jan1day - 1;
      dec31ly.tm_yday = 364 + isleap(dec31ly.tm_year + 1900L);
      weeknum = iso8601wknum(&dec31ly);
    }
    break;
  }
  if (timeptr->tm_mon == 11) {
    int wday, mday;
    wday = timeptr->tm_wday;
    mday = timeptr->tm_mday;
    if ((wday == 1 && (mday >= 29 && mday <= 31)) || (wday == 2 && (mday == 30 || mday == 31)) || (wday == 3 && mday == 31))
      weeknum = 1;
  }
  return weeknum;
}
```