user: 请从给定的汇编指令推导出C源代码：

```asm
<parseLength>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x20,%rsp
  mov    %rdi,-0x18(%rbp)
  movl   $0x0,-0x8(%rbp)
  movl   $0x0,-0x4(%rbp)
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x30,%al
  jne    L37
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  test   %al,%al
  jns    L164
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  and    $0x7f,%eax
  mov    %eax,-0x4(%rbp)
  cmpl   $0x1,-0x4(%rbp)
  jne    L66
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L116
L66:
  cmpl   $0x2,-0x4(%rbp)
  jne    L121
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x8,%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %edx,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L116
L121:
  cmpl   $0x3,-0x4(%rbp)
  jne    L112
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x10,%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x8,%eax
  add    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x4,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %edx,%eax
  mov    %eax,-0x8(%rbp)
  jmp    L116
L112:
  cmpl   $0x4,-0x4(%rbp)
  jne    L116
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x18,%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x10,%eax
  add    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x4,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  shl    $0x8,%eax
  add    %eax,%edx
  mov    -0x18(%rbp),%rax
  add    $0x5,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  add    %edx,%eax
  mov    %eax,-0x8(%rbp)
L116:
  cmpl   $0x0,-0x8(%rbp)
  jle    L89
  mov    -0x4(%rbp),%eax
  add    $0x2,%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x2,%al
  jne    L89
  mov    -0x4(%rbp),%eax
  add    $0x2,%eax
  cltq
  lea    0x1(%rax),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  cmp    $0x1,%al
  jne    L89
  mov    -0x8(%rbp),%eax
  mov    %eax,%ecx
  lea    D16(%rip),%rax
  mov    %rax,%rdx
  lea    D39(%rip),%rax
  mov    %rax,%rsi
  mov    $0xa,%edi
  mov    $0x0,%eax
  call   <writeError@plt>
  jmp    L37
L89:
  lea    D16(%rip),%rax
  mov    %rax,%rdx
  lea    D79(%rip),%rax
  mov    %rax,%rsi
  mov    $0x3,%edi
  mov    $0x0,%eax
  call   <writeError@plt>
  movl   $0xffffffff,-0x8(%rbp)
  jmp    L37
L164:
  mov    -0x18(%rbp),%rax
  add    $0x2,%rax
  movzbl (%rax),%eax
  cmp    $0x2,%al
  jne    L84
  mov    -0x18(%rbp),%rax
  add    $0x3,%rax
  movzbl (%rax),%eax
  cmp    $0x1,%al
  jne    L84
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,-0x8(%rbp)
  mov    -0x8(%rbp),%eax
  mov    %eax,%ecx
  lea    D16(%rip),%rax
  mov    %rax,%rdx
  lea    D34(%rip),%rax
  mov    %rax,%rsi
  mov    $0xa,%edi
  mov    $0x0,%eax
  call   <writeError@plt>
  jmp    L37
L84:
  lea    D16(%rip),%rax
  mov    %rax,%rdx
  lea    D4(%rip),%rax
  mov    %rax,%rsi
  mov    $0x3,%edi
  mov    $0x0,%eax
  call   <writeError@plt>
  movl   $0xffffffff,-0x8(%rbp)
L37:
  mov    -0x8(%rbp),%eax
  leave
  ret
```

tool_calls: name: retrieve_data
arguments: data_label: D16
type_guessed: string
name: retrieve_data
arguments: data_label: D39
type_guessed: string
name: retrieve_data
arguments: data_label: D79
type_guessed: string
name: retrieve_data
arguments: data_label: D34
type_guessed: string
name: retrieve_data
arguments: data_label: D4
type_guessed: string

tool: D16: snmp.mod

tool: D39: [%s] Multi-octet mode length: %d

tool: D79: [%s] Failed to parse length or SNMP version (multi-octet mode).

tool: D34: [%s] Single octet mode length: %d

tool: D4: [%s] Failed to parse length or SNMP version.

assistant: ```c
int parseLength(unsigned char *bufReceive) {
  int nLength = 0;
  int nOctets = 0;
  if (bufReceive[0] == 0x30) {
    if (bufReceive[1] & 0x80) {
      nOctets = bufReceive[1] & 0x7f;
      if (nOctets == 1)
        nLength = bufReceive[2];
      else if (nOctets == 2)
        nLength = (bufReceive[2] << 8) + bufReceive[3];
      else if (nOctets == 3)
        nLength = (bufReceive[2] << 16) + (bufReceive[3] << 8) + bufReceive[4];
      else if (nOctets == 4)
        nLength = (bufReceive[2] << 24) + (bufReceive[3] << 16) + (bufReceive[4] << 8) + bufReceive[5];
      if ((nLength > 0) && ((bufReceive[2 + nOctets] == 0x02) && (bufReceive[2 + nOctets + 1] == 0x01)))
        writeError(10, "[%s] Multi-octet mode length: %d", "snmp.mod", nLength);
      else {
        writeError(3, "[%s] Failed to parse length or SNMP version (multi-octet mode).", "snmp.mod");
        nLength = -1;
      }
    } else if ((bufReceive[2] == 0x02) && (bufReceive[3] == 0x01)) {
      nLength = bufReceive[1];
      writeError(10, "[%s] Single octet mode length: %d", "snmp.mod", nLength);
    } else {
      writeError(3, "[%s] Failed to parse length or SNMP version.", "snmp.mod");
      nLength = -1;
    }
  }
  return nLength;
}
```