Extract string->double and double->string conversions for use in the preparser.

src/conversions.h

Index: src/conversions.h
diff --git a/src/conversions.h b/src/conversions.h
index 4cbeeca828d3ca991df1d22c5555f60c72d941bd..c3e27b2025f519610848fa65d04735a99a1c62cc 100644
--- a/src/conversions.h
+++ b/src/conversions.h
@@ -28,11 +28,36 @@
 #ifndef V8_CONVERSIONS_H_
 #define V8_CONVERSIONS_H_
 
+#include <limits>
+
 #include "scanner-base.h"
 
 namespace v8 {
 namespace internal {
 
+// Maximum number of significant digits in decimal representation.
+// The longest possible double in decimal representation is
+// (2^53 - 1) * 2 ^ -1074 that is (2 ^ 53 - 1) * 5 ^ 1074 / 10 ^ 1074
+// (768 digits). If we parse a number whose first digits are equal to a
+// mean of 2 adjacent doubles (that could have up to 769 digits) the result
+// must be rounded to the bigger one unless the tail consists of zeros, so
+// we don't need to preserve all the digits.
+const int kMaxSignificantDigits = 772;
+
+static const double JUNK_STRING_VALUE =
+    std::numeric_limits<double>::quiet_NaN();
+
+static bool isDigit(int x, int radix) {
+  return (x >= '0' && x <= '9' && x < '0' + radix)
+      || (radix > 10 && x >= 'a' && x < 'a' + radix - 10)
+      || (radix > 10 && x >= 'A' && x < 'A' + radix - 10);
+}
+
+
+static double SignedZero(bool negative) {
+  return negative ? -0.0 : 0.0;
+}
+
 
 // The fast double-to-(unsigned-)int conversion routine does not guarantee
 // rounding towards zero.
@@ -87,17 +112,8 @@ enum ConversionFlags {
 };
 
 
-// Convert from Number object to C integer.
-static inline int32_t NumberToInt32(Object* number);
-static inline uint32_t NumberToUint32(Object* number);
-
-
 // Converts a string into a double value according to ECMA-262 9.3.1
 double StringToDouble(UnicodeCache* unicode_cache,
-                      String* str,
-                      int flags,
-                      double empty_string_val = 0);
-double StringToDouble(UnicodeCache* unicode_cache,
                       Vector<const char> str,
                       int flags,
                       double empty_string_val = 0);
@@ -111,9 +127,6 @@ double StringToDouble(UnicodeCache* unicode_cache,
                       int flags,
                       double empty_string_val = 0);
 
-// Converts a string into an integer.
-double StringToInt(UnicodeCache* unicode_cache, String* str, int radix);
-
 // Converts a double to a string value according to ECMA-262 9.8.1.
 // The buffer should be large enough for any floating point number.
 // 100 characters is enough.