Implemented a parser and updated tiny_obj_loader.cc to use it unless a define is set.

tiny_obj_loader.cc

@@ -22,6 +22,7 @@
 #include <cstdlib>
 #include <cstring>
 #include <cassert>
+#include <cmath>
 
 #include <string>
 #include <vector>
@@ -87,13 +88,165 @@ static inline int parseInt(const char *&token) {
   return i;
 }
 
+
+// Tries to parse a floating point number located at s.
+//
+// s_end should be a location in the string where reading should absolutely
+// stop. For example at the end of the string, to prevent buffer overflows.
+//
+// Parses the following EBNF grammar:
+//   sign    = "+" | "-" ;
+//   END     = ? anything not in digit ?
+//   digit   = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
+//   integer = [sign] , digit , {digit} ;
+//   decimal = integer , ["." , integer] ;
+//   float   = ( decimal , END ) | ( decimal , ("E" | "e") , integer , END ) ;
+//
+//  Valid strings are for example:
+//   -0	 +3.1417e+2  -0.0E-3  1.0324  -1.41   11e2
+//
+// If the parsing is a success, result is set to the parsed value and true 
+// is returned.
+//
+// The function is greedy and will parse until any of the following happens:
+//  - a non-conforming character is encountered.
+//  - s_end is reached.
+//
+// The following situations triggers a failure:
+//  - s >= s_end.
+//  - parse failure.
+// 
+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;
+
+	/*
+		BEGIN PARSING.
+	*/
+
+	// Find out what sign we've got.
+	if (*curr == '+' || *curr == '-')
+	{
+		sign = *curr;
+		curr++;
+	}
+	else if (isdigit(*curr)) { /* Pass through. */ }
+	else
+	{
+		goto fail;
+	}
+
+	// Read the integer part.
+	while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
+	{
+		mantissa *= 10;
+		mantissa += static_cast<int>(*curr - 0x30);
+		curr++;	read++;
+	}
+
+	// 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;
+		while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
+		{
+			// NOTE: Don't use powf here, it will absolutely murder precision.
+			mantissa += static_cast<int>(*curr - 0x30) * pow(10, -read);
+			read++; curr++;
+		}
+	}
+	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.
+		if ((end_not_reached = (curr != s_end)) && (*curr == '+' || *curr == '-'))
+		{
+			exp_sign = *curr;
+			curr++;
+		}
+		else if (isdigit(*curr)) { /* Pass through. */ }
+		else
+		{
+			// Empty E is not allowed.
+			goto fail;
+		}
+
+		read = 0;
+		while ((end_not_reached = (curr != s_end)) && isdigit(*curr))
+		{
+			exponent *= 10;
+			exponent += static_cast<int>(*curr - 0x30);
+			curr++;	read++;
+		}
+		exponent *= (exp_sign == '+'? 1 : -1);
+		if (read == 0)
+			goto fail;
+	}
+
+assemble:
+	*result = (sign == '+'? 1 : -1) * ldexp(mantissa * pow(5, exponent), exponent);
+	return true;
+fail:
+	return false;
+}
 static inline float parseFloat(const char *&token) {
   token += strspn(token, " \t");
+#ifdef TINY_OBJ_LOADER_OLD_FLOAT_PARSER
   float f = (float)atof(token);
   token += strcspn(token, " \t\r");
+#else
+  const char *end = token + strcspn(token, " \t\r");
+  double val = 0.0;
+  tryParseDouble(token, end, &val);
+  float f = static_cast<float>(val);
+  token = end;
+#endif
   return f;
 }
 
+
 static inline void parseFloat2(float &x, float &y, const char *&token) {
   x = parseFloat(token);
   y = parseFloat(token);