user: What is the c source code of the assembly code below:

```asm
<epr_str_tok_tok>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x18,%rsp
  mov    %rdi,%rbp
  mov    %rsi,%r12
  mov    %rdx,%r14
  mov    %rcx,%r13
  test   %rdi,%rdi
  setne  %dil
  movzbl %dil,%edi
  call   <assert@plt>
  mov    0x0(%r13),%r15
  mov    %rbp,%rdi
  call   <strlen@plt>
  cmp    %rax,%r15
  jae    L59
  lea    0x0(%rbp,%r15,1),%rax
  mov    %rax,0x8(%rsp)
  movzbl (%rax),%esi
  test   %sil,%sil
  je     L50
  mov    %r15,%rbx
  jmp    L10
L143:
  mov    $0x0,%ebx
L39:
  mov    %rbx,%r14
  sub    0x0(%r13),%r14
  mov    %r14,%rdi
  call   <epr_create_string@plt>
  mov    %rax,%r12
  mov    %rbp,%rsi
  add    0x0(%r13),%rsi
  mov    %r14,%rdx
  mov    %rax,%rdi
  call   <strncpy@plt>
  movb   $0x0,(%r12,%r14,1)
  add    $0x1,%rbx
  mov    %rbx,0x0(%r13)
L20:
  mov    %r12,%rax
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L138:
  add    $0x1,%rbx
  movzbl 0x0(%rbp,%rbx,1),%esi
  test   %sil,%sil
  je     L105
L10:
  movsbl %sil,%esi
  mov    %r12,%rdi
  call   <strchr@plt>
  test   %rbx,%rbx
  jne    L139
  test   %rax,%rax
  jne    L143
L139:
  movsbl 0x0(%rbp,%rbx,1),%esi
  mov    %r12,%rdi
  call   <strchr@plt>
  test   %rbx,%rbx
  je     L138
  test   %rax,%rax
  je     L138
  movsbl -0x1(%rbp,%rbx,1),%esi
  mov    %r14,%rdi
  call   <strchr@plt>
  test   %rax,%rax
  jne    L138
  jmp    L39
L50:
  mov    %r15,%rbx
L105:
  mov    %rbp,%rdi
  call   <strlen@plt>
  mov    $0x0,%r12d
  test   %rax,%rax
  jle    L20
  test   %r15,%r15
  jne    L94
  add    $0x1,%rbx
  mov    %rbx,0x0(%r13)
  mov    0x8(%rsp),%rdi
  call   <epr_clone_string@plt>
  mov    %rax,%r12
  jmp    L20
L94:
  sub    %r15,%rbx
  mov    %rbx,%rdi
  call   <epr_create_string@plt>
  mov    %rax,%r12
  mov    %rbp,%rsi
  add    0x0(%r13),%rsi
  mov    %rbx,%rdx
  mov    %rax,%rdi
  call   <strncpy@plt>
  movb   $0x0,(%r12,%rbx,1)
  mov    %rbp,%rdi
  call   <strlen@plt>
  cltq
  mov    %rax,0x0(%r13)
  jmp    L20
L59:
  mov    $0x0,%r12d
  jmp    L20
```

assistant: ```c
char *epr_str_tok_tok(const char *str, const char *seps, const char *exceptions, uint *pos) {
  char *token = NULL;
  uint i, old_pos;
  uint token_len = 0;
  assert(str != NULL);
  if (*pos >= (uint)strlen(str))
    return NULL;
  old_pos = *pos;
  for (i = *pos; str[i] != '\0'; i++) {
    if (((strchr(seps, str[i]) != NULL) && (i == 0)) || ((strchr(seps, str[i]) != NULL) && (i > 0) && (strchr(exceptions, str[i - 1]) == NULL))) {
      token_len = i - *pos;
      token = epr_create_string(token_len);
      strncpy(token, str + *pos, token_len);
      token[token_len] = '\0';
      *pos = i + 1;
      return token;
    }
  }
  if (strlen(str) > 0) {
    if (old_pos == 0) {
      *pos = i + 1;
      token = epr_clone_string(str);
      return token;
    } else if (old_pos > 0) {
      token_len = i - old_pos;
      token = epr_create_string(token_len);
      strncpy(token, str + *pos, token_len);
      token[token_len] = '\0';
      *pos = (int)strlen(str);
      return token;
    }
  }
  return NULL;
}
```