From fad03b44a0a09cb02f01427c14196d05a373e1c5 Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Thu, 29 Jul 1999 10:00:22 +0000
Subject: [PATCH] [project @ 1999-07-29 10:00:22 by simonmar] Shift operations
where the shift count is greater than the width of the type being shifted are
now defined as returning zero (or -1 in the case of a negative integer being
shifted right with iShiftRA).
---
ghc/includes/PrimOps.h | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/ghc/includes/PrimOps.h b/ghc/includes/PrimOps.h
index d5bb117f51a4..6ae67dbfc0ab 100644
--- a/ghc/includes/PrimOps.h
+++ b/ghc/includes/PrimOps.h
@@ -1,5 +1,5 @@
/* -----------------------------------------------------------------------------
- * $Id: PrimOps.h,v 1.32 1999/06/25 10:09:19 panne Exp $
+ * $Id: PrimOps.h,v 1.33 1999/07/29 10:00:22 simonmar Exp $
*
* (c) The GHC Team, 1998-1999
*
@@ -195,15 +195,21 @@ typedef union {
#define xorzh(r,a,b) r=(a)^(b)
#define notzh(r,a) r=~(a)
-#define shiftLzh(r,a,b) r=(a)<<(b)
-#define shiftRLzh(r,a,b) r=(a)>>(b)
-#define iShiftLzh(r,a,b) r=(a)<<(b)
+/* The extra tests below properly define the behaviour when shifting
+ * by offsets larger than the width of the value being shifted. Doing
+ * so is undefined in C (and in fact gives different answers depending
+ * on whether the operation is constant folded or not with gcc on x86!)
+ */
+
+#define shiftLzh(r,a,b) r=((b) >= BITS_IN(W_)) ? 0 : (a)<<(b)
+#define shiftRLzh(r,a,b) r=((b) >= BITS_IN(W_)) ? 0 : (a)>>(b)
+#define iShiftLzh(r,a,b) r=((b) >= BITS_IN(W_)) ? 0 : (a)<<(b)
/* Right shifting of signed quantities is not portable in C, so
the behaviour you'll get from using these primops depends
on the whatever your C compiler is doing. ToDo: fix/document. -- sof 8/98
*/
-#define iShiftRAzh(r,a,b) r=(a)>>(b)
-#define iShiftRLzh(r,a,b) r=(a)>>(b)
+#define iShiftRAzh(r,a,b) r=((b) >= BITS_IN(I_)) ? (((a) < 0) ? -1 : 0) : (a)>>(b)
+#define iShiftRLzh(r,a,b) r=((b) >= BITS_IN(I_)) ? 0 : ((W_)(a))>>(b)
#define int2Wordzh(r,a) r=(W_)(a)
#define word2Intzh(r,a) r=(I_)(a)
--
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