Avoid undefined behavior regarding signed integers and left shifts.

[bpt/guile.git] / libguile / vm-i-scheme.c

diff --git a/libguile/vm-i-scheme.c b/libguile/vm-i-scheme.c
index fc32ec5..587aa95 100644 (file)
--- a/libguile/vm-i-scheme.c
+++ b/libguile/vm-i-scheme.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 2001, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc.
+/* Copyright (C) 2001, 2009, 2010, 2011, 2012, 2013,
+ *   2014 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -236,10 +237,12 @@ VM_DEFINE_FUNCTION (149, ge, "ge?", 2)
 #if SCM_GNUC_PREREQ (4, 5) && (defined __x86_64__ || defined __i386__)
 
 # undef _CX
-# ifdef __x86_64__
+# if SIZEOF_VOID_P == 8
 #  define _CX "rcx"
-# else
+# elif SIZEOF_VOID_P == 4
 #  define _CX "ecx"
+# else
+#  error unsupported word size
 # endif
 
 /* The macros below check the CPU's overflow flag to improve fixnum
@@ -503,7 +506,9 @@ VM_DEFINE_FUNCTION (159, ash, "ash", 2)
               && ((scm_t_bits)
                   (SCM_SRS (nn, (SCM_I_FIXNUM_BIT-1 - bits_to_shift)) + 1)
                   <= 1))
-            RETURN (SCM_I_MAKINUM (nn << bits_to_shift));
+            RETURN (SCM_I_MAKINUM (nn < 0
+                                   ? -(-nn << bits_to_shift)
+                                   : (nn << bits_to_shift)));
           /* fall through */
         }
       /* fall through */