From d935129a2c3dd7d745d8ee16956db1258491a7f9 Mon Sep 17 00:00:00 2001
From: Walter Bright <walter@walterbright.com>
Date: Mon, 19 Oct 2015 12:13:19 -0700
Subject: [PATCH] lexer.d: avoid expensive overflow check

---
 src/lexer.d | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/src/lexer.d b/src/lexer.d
index 01aec16221c7..f164387ef51c 100644
--- a/src/lexer.d
+++ b/src/lexer.d
@@ -1832,16 +1832,14 @@ public:
             default:
                 goto Ldone;
             }
-            uinteger_t n2 = n * base;
-            if ((n2 / base != n || n2 + d < n))
-            {
-                overflow = true;
-            }
-            n = n2 + d;
-            // if n needs more than 64 bits
-            if (n.sizeof > 8 && n > 0xFFFFFFFFFFFFFFFFUL)
+            // Avoid expensive overflow check if we aren't at risk of overflow
+            if (n <= 0x0FFF_FFFF_FFFF_FFFFUL)
+                n = n * base + d;
+            else
             {
-                overflow = true;
+                import core.checkedint;
+                n = mulu(n, base, overflow);
+                n = addu(n, d, overflow);
             }
         }
     Ldone: