Simplify logic in string-to-double conversion code....

src/conversions.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 251 matching lines @@
                                      int flags,
                                      double empty_string_val) {
   double result = 0.0;
   int index = 0;
 
   int len = GetLength(str);
 
   // Skip leading spaces.
   while ((index < len) && IsSpace(str, index)) index++;
 
-  // Compute sign of result.
+  // Is the string empty?
+  if (index >= len) return empty_string_val;
+
+  // Get the first character.
+  uint16_t fst = GetChar(str, index);
+
+  // Numbers can only start with '-', '+', '.', 'I' (Infinity), or a digit.
+  if (fst != '-' && fst != '+' && fst != '.' && fst != 'I' &&
+      (fst > '9' || fst < '0')) {
+    return JUNK_STRING_VALUE;
+  }
+
+  // Compute sign of result based on first character.
   int sign = 1;
-  if (index < len && GetChar(str, index) == '-') {
+  if (fst == '-') {
     sign = -1;
     index++;
     // String only containing a '-' are junk chars.
     if (index == len) return JUNK_STRING_VALUE;
   }
 
-  // string is empty?
-  if (index >= len) return empty_string_val;
-
   // do we have a hex number?
   // (since the string is 0-terminated, it's ok to look one char beyond the end)
   if ((flags & ALLOW_HEX) != 0 &&
       (index + 1) < len &&
       GetChar(str, index) == '0' &&
       (GetChar(str, index + 1) == 'x' || GetChar(str, index + 1) == 'X')) {
     index += 2;
     index = StringToInt(str, index, 16, &result);
   } else if ((flags & ALLOW_OCTALS) != 0 && ShouldParseOctal(str, index)) {
     // NOTE: We optimistically try to parse the number as an octal (if
@@ skipping 390 matching lines @@
   // Allocate result and fill in the parts.
   StringBuilder builder(result_size + 1);
   builder.AddSubstring(integer_buffer + integer_pos + 1, integer_part_size);
   if (decimal_pos > 0) builder.AddCharacter('.');
   builder.AddSubstring(decimal_buffer, decimal_pos);
   return builder.Finalize();
 }
 
 
 } }  // namespace v8::internal