[regexp] move regexp parser into own files.

src/utils.h

Index: src/utils.h
diff --git a/src/utils.h b/src/utils.h
index ce62c81b8c0128dd46ef8b0262cffb16d5a745ff..1ea2d56fbfd44c4b139871bd29fd64cac104eb1d 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -26,6 +26,16 @@ namespace internal {
 // ----------------------------------------------------------------------------
 // General helper functions
 
+// Returns the value (0 .. 15) of a hexadecimal character c.
+// If c is not a legal hexadecimal character, returns a value < 0.
+inline int HexValue(uc32 c) {
+  c -= '0';
+  if (static_cast<unsigned>(c) <= 9) return c;
+  c = (c | 0x20) - ('a' - '0');  // detect 0x11..0x16 and 0x31..0x36.
+  if (static_cast<unsigned>(c) <= 5) return c + 10;
+  return -1;
+}
+
 
 inline int BoolToInt(bool b) { return b ? 1 : 0; }