Function fixIndex

source/external/tinyobj/tiny_obj_loader.h:830–863

Make index zero-base, and also support relative index.

// Make index zero-base, and also support relative index.
static inline bool fixIndex(int idx, int n, int *ret, bool allow_zero,
                            const warning_context &context) {
  if (!ret) {
    return false;
  }

  if (idx > 0) {
    (*ret) = idx - 1;
    return true;
  }

  if (idx == 0) {
    // zero is not allowed according to the spec.
    if (context.warn) {
      (*context.warn) +=
          "A zero value index found (will have a value of -1 for normal and "
          "tex indices. Line " +
          toString(context.line_number) + ").\n";
    }

    (*ret) = idx - 1;
    return allow_zero;
  }

  if (idx < 0) {
    (*ret) = n + idx;  // negative value = relative
    if ((*ret) < 0) {
      return false;  // invalid relative index
    }
    return true;
  }

  return false;  // never reach here.
}

static inline std::string parseString(const char **token) {
  std::string s;