utils.h

#ifdef TINYOBJLOADER_USE_DOUBLE
//#pragma message "using double"
typedef double real_t;
#else
//#pragma message "using float"
typedef float real_t;
#endif

#if __cplusplus > 199711L
#define TINYOBJ_OVERRIDE override
#else
#define TINYOBJ_OVERRIDE
#endif

#include <map>
#include <string>
#include <vector>
#include <iostream>
#include <fstream>
#include <sstream>
#include <assert.h>

#define IS_SPACE(x) (((x) == ' ') || ((x) == '\t'))
#define IS_DIGIT(x) \
  (static_cast<unsigned int>((x) - '0') < static_cast<unsigned int>(10))
#define IS_NEW_LINE(x) (((x) == '\r') || ((x) == '\n') || ((x) == '\0'))

struct vertex_index_t {
  int v_idx, vt_idx, vn_idx;
vertex_index_t() : v_idx(-1), vt_idx(-1), vn_idx(-1) {}
  explicit vertex_index_t(int idx) : v_idx(idx), vt_idx(idx), vn_idx(idx) {}
  vertex_index_t(int vidx, int vtidx, int vnidx)
  : v_idx(vidx), vt_idx(vtidx), vn_idx(vnidx) {}
};

struct face_t {
  unsigned int
  smoothing_group_id;  // smoothing group id. 0 = smoothing groupd is off.
  int pad_;
  std::vector<vertex_index_t> vertex_indices;  // face vertex indices.

face_t() : smoothing_group_id(0), pad_(0) {}
};

static void SplitString(const std::string &s, char delim, char escape,
                        std::vector<std::string> &elems) {
  std::string token;

  bool escaping = false;
  for (size_t i = 0; i < s.size(); ++i) {
    char ch = s[i];
    if (escaping) {
      escaping = false;
    } else if (ch == escape) {
      escaping = true;
      continue;
    } else if (ch == delim) {
      if (!token.empty()) {
        elems.push_back(token);
      }
      token.clear();
      continue;
    }
    token += ch;
  }

  elems.push_back(token);
}

static bool tryParseDouble(const char *s, const char *s_end, double *result) {
  if (s >= s_end) {
    return false;
  }

  double mantissa = 0.0;
  // This exponent is base 2 rather than 10.
  // However the exponent we parse is supposed to be one of ten,
  // thus we must take care to convert the exponent/and or the
  // mantissa to a * 2^E, where a is the mantissa and E is the
  // exponent.
  // To get the final double we will use ldexp, it requires the
  // exponent to be in base 2.
  int exponent = 0;

  // NOTE: THESE MUST BE DECLARED HERE SINCE WE ARE NOT ALLOWED
  // TO JUMP OVER DEFINITIONS.
  char sign = '+';
  char exp_sign = '+';
  char const *curr = s;

  // How many characters were read in a loop.
  int read = 0;
  // Tells whether a loop terminated due to reaching s_end.
  bool end_not_reached = false;
  bool leading_decimal_dots = false;

  /*
          BEGIN PARSING.
  */

  // Find out what sign we've got.
  if (*curr == '+' || *curr == '-') {
    sign = *curr;
    curr++;
    if ((curr != s_end) && (*curr == '.')) {
      // accept. Somethig like `.7e+2`, `-.5234`
      leading_decimal_dots = true;
    }
  } else if (IS_DIGIT(*curr)) { /* Pass through. */
  } else if (*curr == '.') {
    // accept. Somethig like `.7e+2`, `-.5234`
    leading_decimal_dots = true;
  } else {
    goto fail;
  }

  // Read the integer part.
  end_not_reached = (curr != s_end);
  if (!leading_decimal_dots) {
    while (end_not_reached && IS_DIGIT(*curr)) {
      mantissa *= 10;
      mantissa += static_cast<int>(*curr - 0x30);
      curr++;
      read++;
      end_not_reached = (curr != s_end);
    }

    // We must make sure we actually got something.
    if (read == 0) goto fail;
  }

  // We allow numbers of form "#", "###" etc.
  if (!end_not_reached) goto assemble;

  // Read the decimal part.
  if (*curr == '.') {
    curr++;
    read = 1;
    end_not_reached = (curr != s_end);
    while (end_not_reached && IS_DIGIT(*curr)) {
      static const double pow_lut[] = {
	1.0, 0.1, 0.01, 0.001, 0.0001, 0.00001, 0.000001, 0.0000001,
      };
      const int lut_entries = sizeof pow_lut / sizeof pow_lut[0];

      // NOTE: Don't use powf here, it will absolutely murder precision.
      mantissa += static_cast<int>(*curr - 0x30) *
	(read < lut_entries ? pow_lut[read] : std::pow(10.0, -read));
      read++;
      curr++;
      end_not_reached = (curr != s_end);
    }
  } else if (*curr == 'e' || *curr == 'E') {
  } else {
    goto assemble;
  }

  if (!end_not_reached) goto assemble;

  // Read the exponent part.
  if (*curr == 'e' || *curr == 'E') {
    curr++;
    // Figure out if a sign is present and if it is.
    end_not_reached = (curr != s_end);
    if (end_not_reached && (*curr == '+' || *curr == '-')) {
      exp_sign = *curr;
      curr++;
    } else if (IS_DIGIT(*curr)) { /* Pass through. */
    } else {
      // Empty E is not allowed.
      goto fail;
    }

    read = 0;
    end_not_reached = (curr != s_end);
    while (end_not_reached && IS_DIGIT(*curr)) {
      // To avoid annoying MSVC's min/max macro definiton,
      // Use hardcoded int max value
      if (exponent > (2147483647/10)) { // 2147483647 = std::numeric_limits<int>::max()
        // Integer overflow
        goto fail;
      }
      exponent *= 10;
      exponent += static_cast<int>(*curr - 0x30);
      curr++;
      read++;
      end_not_reached = (curr != s_end);
    }
    exponent *= (exp_sign == '+' ? 1 : -1);
    if (read == 0) goto fail;
  }

 assemble:
  *result = (sign == '+' ? 1 : -1) *
    (exponent ? std::ldexp(mantissa * std::pow(5.0, exponent), exponent)
     : mantissa);
  return true;
 fail:
  return false;
}

static inline real_t parseReal(const char **token, double default_value = 0.0) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");
  double val = default_value;
  tryParseDouble((*token), end, &val);
  real_t f = static_cast<real_t>(val);
  (*token) = end;
  return f;
}

static inline bool parseReal(const char **token, real_t *out) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");
  double val;
  bool ret = tryParseDouble((*token), end, &val);
  if (ret) {
    real_t f = static_cast<real_t>(val);
    (*out) = f;
  }
  (*token) = end;
  return ret;
}

static inline void parseReal2(real_t *x, real_t *y, const char **token,
                              const double default_x = 0.0,
                              const double default_y = 0.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
}

static inline void parseReal3(real_t *x, real_t *y, real_t *z,
                              const char **token, const double default_x = 0.0,
                              const double default_y = 0.0,
                              const double default_z = 0.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
  (*z) = parseReal(token, default_z);
}

static inline void parseV(real_t *x, real_t *y, real_t *z, real_t *w,
                          const char **token, const double default_x = 0.0,
                          const double default_y = 0.0,
                          const double default_z = 0.0,
                          const double default_w = 1.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
  (*z) = parseReal(token, default_z);
  (*w) = parseReal(token, default_w);
}

// Extension: parse vertex with colors(6 items)
static inline bool parseVertexWithColor(real_t *x, real_t *y, real_t *z,
                                        real_t *r, real_t *g, real_t *b,
                                        const char **token,
                                        const double default_x = 0.0,
                                        const double default_y = 0.0,
                                        const double default_z = 0.0) {
  (*x) = parseReal(token, default_x);
  (*y) = parseReal(token, default_y);
  (*z) = parseReal(token, default_z);

  const bool found_color =
    parseReal(token, r) && parseReal(token, g) && parseReal(token, b);

  if (!found_color) {
    (*r) = (*g) = (*b) = 1.0;
  }

  return found_color;
}

static inline bool parseOnOff(const char **token, bool default_value = true) {
  (*token) += strspn((*token), " \t");
  const char *end = (*token) + strcspn((*token), " \t\r");

  bool ret = default_value;
  if ((0 == strncmp((*token), "on", 2))) {
    ret = true;
  } else if ((0 == strncmp((*token), "off", 3))) {
    ret = false;
  }

  (*token) = end;
  return ret;
}

static inline bool fixIndex(int idx, int n, int *ret) {
  if (!ret) {
    return false;
  }

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

  if (idx == 0) {
    // zero is not allowed according to the spec.
    return false;
  }

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

  return false;  // never reach here.
}

static bool parseTriple(const char **token, int vsize, int vnsize, int vtsize,
                        vertex_index_t *ret) {
  if (!ret) {
    return false;
  }

  vertex_index_t vi(-1);

  if (!fixIndex(atoi((*token)), vsize, &(vi.v_idx))) {
    return false;
  }

  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    (*ret) = vi;
    return true;
  }
  (*token)++;

  // i//k
  if ((*token)[0] == '/') {
    (*token)++;
    if (!fixIndex(atoi((*token)), vnsize, &(vi.vn_idx))) {
      return false;
    }
    (*token) += strcspn((*token), "/ \t\r");
    (*ret) = vi;
    return true;
  }

  // i/j/k or i/j
  if (!fixIndex(atoi((*token)), vtsize, &(vi.vt_idx))) {
    return false;
  }

  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    (*ret) = vi;
    return true;
  }

  // i/j/k
  (*token)++;  // skip '/'
  if (!fixIndex(atoi((*token)), vnsize, &(vi.vn_idx))) {
    return false;
  }
  (*token) += strcspn((*token), "/ \t\r");

  (*ret) = vi;

  return true;
}

static vertex_index_t parseRawTriple(const char **token) {
  vertex_index_t vi(static_cast<int>(0));  // 0 is an invalid index in OBJ

  vi.v_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }
  (*token)++;

  // i//k
  if ((*token)[0] == '/') {
    (*token)++;
    vi.vn_idx = atoi((*token));
    (*token) += strcspn((*token), "/ \t\r");
    return vi;
  }

  // i/j/k or i/j
  vi.vt_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  if ((*token)[0] != '/') {
    return vi;
  }

  // i/j/k
  (*token)++;  // skip '/'
  vi.vn_idx = atoi((*token));
  (*token) += strcspn((*token), "/ \t\r");
  return vi;
}

static inline std::string parseString(const char **token) {
  std::string s;
  (*token) += strspn((*token), " \t");
  size_t e = strcspn((*token), " \t\r");
  s = std::string((*token), &(*token)[e]);
  (*token) += e;
  return s;
}

static inline int parseInt(const char **token) {
  (*token) += strspn((*token), " \t");
  int i = atoi((*token));
  (*token) += strcspn((*token), " \t\r");
  return i;
}

static std::istream &safeGetline(std::istream &is, std::string &t) {
  t.clear();

  // The characters in the stream are read one-by-one using a std::streambuf.
  // That is faster than reading them one-by-one using the std::istream.
  // Code that uses streambuf this way must be guarded by a sentry object.
  // The sentry object performs various tasks,
  // such as thread synchronization and updating the stream state.

  std::istream::sentry se(is, true);
  std::streambuf *sb = is.rdbuf();

  if (se) {
    for (;;) {
      int c = sb->sbumpc();
      switch (c) {
      case '\n':
	return is;
      case '\r':
	if (sb->sgetc() == '\n') sb->sbumpc();
	return is;
      case EOF:
	// Also handle the case when the last line has no line ending
	if (t.empty()) is.setstate(std::ios::eofbit);
	return is;
      default:
	t += static_cast<char>(c);
      }
    }
  }

  return is;
}