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

```asm
<_atob>:
  endbr64
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  mov    %rdi,%rbx
  sub    $0x30,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x28(%rsp)
  xor    %eax,%eax
  cmpb   $0x30,(%rsi)
  je     L207
L194:
  cmp    $0x10,%edx
  je     L81
L43:
  movl   $0x0,(%rbx)
  movzbl 0x0(%rbp),%ecx
  xor    %esi,%esi
  test   %cl,%cl
  jne    L168
  jmp    L164
  nopl   (%rax)
L89:
  movsbl %al,%eax
L113:
  cmp    %edx,%eax
  jge    L167
L144:
  imul   %edx,%esi
  movzbl 0x1(%rbp),%ecx
  add    $0x1,%rbp
  add    %eax,%esi
  test   %cl,%cl
  je     L164
L168:
  lea    -0x30(%rcx),%eax
  cmp    $0x9,%al
  jbe    L89
  lea    -0x61(%rcx),%eax
  cmp    $0x5,%al
  ja     L37
  sub    $0x57,%ecx
  movsbl %cl,%eax
  cmp    %edx,%eax
  jl     L144
  nopl   0x0(%rax)
L167:
  xor    %eax,%eax
L82:
  mov    0x28(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L157
  add    $0x30,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  ret
  nopl   0x0(%rax,%rax,1)
L37:
  lea    -0x41(%rcx),%eax
  cmp    $0x5,%al
  ja     L167
  sub    $0x37,%ecx
  movsbl %cl,%eax
  jmp    L113
  nop
L207:
  movzbl 0x1(%rsi),%eax
  and    $0xffffffdf,%eax
  cmp    $0x58,%al
  jne    L194
  add    $0x2,%rbp
L81:
  mov    $0x2e,%esi
  mov    %rbp,%rdi
  call   <strchr@plt>
  mov    %rax,%r12
  test   %rax,%rax
  je     L159
  mov    %rax,%r13
  sub    %rbp,%r13
  cmp    $0x13,%r13
  ja     L167
  lea    0x10(%rsp),%r14
  mov    %r13d,%edx
  mov    %rbp,%rsi
  mov    %r14,%rdi
  call   <strncpy@plt>
  lea    0x8(%rsp),%rdi
  mov    $0x10,%edx
  mov    %r14,%rsi
  movb   $0x0,0x10(%rsp,%r13,1)
  call   <_atob>
  test   %eax,%eax
  je     L167
  add    $0x1,%r12
  mov    $0x2e,%esi
  mov    %r12,%rdi
  call   <strchr@plt>
  test   %rax,%rax
  jne    L167
  lea    0xc(%rsp),%rdi
  mov    $0x10,%edx
  mov    %r12,%rsi
  call   <_atob>
  test   %eax,%eax
  je     L167
  mov    0x8(%rsp),%eax
  shl    $0x10,%eax
  add    0xc(%rsp),%eax
  mov    %eax,(%rbx)
  mov    $0x1,%eax
  jmp    L82
  cs nopw 0x0(%rax,%rax,1)
L164:
  mov    %esi,(%rbx)
  mov    $0x1,%eax
  jmp    L82
  nopl   0x0(%rax)
L159:
  mov    $0x10,%edx
  jmp    L43
L157:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
int _atob(uint64_t *vp, char *p, int base) {
  uint64_t value, v1, v2;
  char *q, tmp[20];
  int digit;
  if (p[0] == '0' && (p[1] == 'x' || p[1] == 'X')) {
    base = 16;
    p += 2;
  }
  if (base == 16 && (q = strchr(p, '.')) != 0) {
    if (q - p > sizeof(tmp) - 1)
      return (0);
    strncpy(tmp, p, q - p);
    tmp[q - p] = '\0';
    if (!_atob(&v1, tmp, 16))
      return (0);
    q++;
    if (strchr(q, '.'))
      return (0);
    if (!_atob(&v2, q, 16))
      return (0);
    *vp = (v1 << 16) + v2;
    return (1);
  }
  value = *vp = 0;
  for (; *p; p++) {
    if (*p >= '0' && *p <= '9')
      digit = *p - '0';
    else if (*p >= 'a' && *p <= 'f')
      digit = *p - 'a' + 10;
    else if (*p >= 'A' && *p <= 'F')
      digit = *p - 'A' + 10;
    else
      return (0);
    if (digit >= base)
      return (0);
    value *= base;
    value += digit;
  }
  *vp = value;
  return (1);
}
```