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Avoid undefined behavior regarding signed integers and left shifts.

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* libguile/numbers.c (scm_logbit_p): If the requested bit is the sign
  bit (or above), check the sign portably.  Otherwise, ensure that we're
  testing the bit in a two's complement representation.
  (left_shift_exact_integer): Avoid left-shifting negative integers.

* libguile/vm-i-scheme.c (ash): Avoid left-shifting negative integers.
This commit is contained in:
Mark H Weaver 2014-03-11 20:19:17 -04:00
parent 5fbf0e0f99
commit 03cce0ce5f
2 changed files with 17 additions and 8 deletions
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18
libguile/numbers.c
View file

@ -1,6 +1,6 @@
/* Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
* 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012,
* 2013 Free Software Foundation, Inc.
* 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013,
* 2014 Free Software Foundation, Inc.
*
* Portions Copyright 1990, 1991, 1992, 1993 by AT&T Bell Laboratories
* and Bellcore. See scm_divide.
@ -4680,9 +4680,15 @@ SCM_DEFINE (scm_logbit_p, "logbit?", 2, 0, 0,
if (SCM_I_INUMP (j))
{
/* bits above what's in an inum follow the sign bit */
iindex = min (iindex, SCM_LONG_BIT - 1);
return scm_from_bool ((1L << iindex) & SCM_I_INUM (j));
if (iindex < SCM_LONG_BIT - 1)
/* Arrange for the number to be converted to unsigned before
checking the bit, to ensure that we're testing the bit in a
two's complement representation (regardless of the native
representation. */
return scm_from_bool ((1UL << iindex) & SCM_I_INUM (j));
else
/* Portably check the sign. */
return scm_from_bool (SCM_I_INUM (j) < 0);
}
else if (SCM_BIGP (j))
{
@ -4992,7 +4998,7 @@ left_shift_exact_integer (SCM n, long count)
else if (count < SCM_I_FIXNUM_BIT-1 &&
((scm_t_bits) (SCM_SRS (nn, (SCM_I_FIXNUM_BIT-1 - count)) + 1)
<= 1))
return SCM_I_MAKINUM (nn << count);
return SCM_I_MAKINUM (nn < 0 ? -(-nn << count) : (nn << count));
else
{
SCM result = scm_i_inum2big (nn);

7
libguile/vm-i-scheme.c
View file

@ -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
@ -505,7 +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 */