From: simonmar <unknown>
Date: Mon, 1 Jul 2002 11:37:35 +0000 (+0000)
Subject: [project @ 2002-07-01 11:37:35 by simonmar]
X-Git-Tag: nhc98-1-18-release~960
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=1702d51a5974c23f8de861a0c01fc2925fed4477;p=ghc-base.git

[project @ 2002-07-01 11:37:35 by simonmar]
Replace divInt# with a version which doesn't suffer from overflow
problems (thanks to Dylan Thurston for the code).
---

diff --git a/GHC/Base.lhs b/GHC/Base.lhs
index 8abd593..3945397 100644
--- a/GHC/Base.lhs
+++ b/GHC/Base.lhs
@@ -644,11 +644,18 @@ data (:*:) a b = a :*: b
 %*********************************************************
 
 \begin{code}
-divInt#, modInt# :: Int# -> Int# -> Int#
+divInt# :: Int# -> Int# -> Int#
 x# `divInt#` y#
-    | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
-    | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
+	-- careful NOT to overflow if we do any additional arithmetic
+	-- on the arguments...  the following  previous version of this
+	-- code has problems with overflow:
+--    | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
+--    | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
+    | (x# ># 0#) && (y# <# 0#) = (x# -# 1#) `quotInt#` y# -# 1#
+    | (x# <# 0#) && (y# ># 0#) = (x# +# 1#) `quotInt#` y# -# 1#
     | otherwise                = x# `quotInt#` y#
+
+modInt# :: Int# -> Int# -> Int#
 x# `modInt#` y#
     | (x# ># 0#) && (y# <# 0#) ||
       (x# <# 0#) && (y# ># 0#)    = if r# /=# 0# then r# +# y# else 0#