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VM: Avoid signed overflows in 'add1' and 'sub1'.

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* libguile/vm-i-scheme.c (INUM_STEP): New macro.
  (add1, sub1): Avoid signed overflows, and use INUM_STEP.
This commit is contained in:
Mark H Weaver 2013-08-03 14:46:40 -04:00
parent 478fa0d530
commit cb1482e719
1 changed files with 14 additions and 12 deletions
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26
libguile/vm-i-scheme.c
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@ -207,10 +207,14 @@ VM_DEFINE_FUNCTION (149, ge, "ge?", 2)
/* The maximum/minimum tagged integers. */
#undef INUM_MAX
#undef INUM_MIN
#undef INUM_STEP
#define INUM_MAX \
((scm_t_signed_bits) SCM_UNPACK (SCM_I_MAKINUM (SCM_MOST_POSITIVE_FIXNUM)))
#define INUM_MIN \
((scm_t_signed_bits) SCM_UNPACK (SCM_I_MAKINUM (SCM_MOST_NEGATIVE_FIXNUM)))
#define INUM_STEP \
((scm_t_signed_bits) SCM_UNPACK (SCM_INUM1) \
- (scm_t_signed_bits) SCM_UNPACK (SCM_INUM0))
#undef FUNC2
#define FUNC2(CFUNC,SFUNC) \
@ -294,15 +298,14 @@ VM_DEFINE_FUNCTION (151, add1, "add1", 1)
{
ARGS1 (x);
/* Check for overflow. */
if (SCM_LIKELY ((scm_t_intptr) SCM_UNPACK (x) < INUM_MAX))
/* Check for overflow. We must avoid overflow in the signed
addition below, even if X is not an inum. */
if (SCM_LIKELY ((scm_t_signed_bits) SCM_UNPACK (x) <= INUM_MAX - INUM_STEP))
{
SCM result;
/* Add the integers without untagging. */
result = SCM_PACK ((scm_t_intptr) SCM_UNPACK (x)
+ (scm_t_intptr) SCM_UNPACK (SCM_I_MAKINUM (1))
- scm_tc2_int);
/* Add 1 to the integer without untagging. */
result = SCM_PACK ((scm_t_signed_bits) SCM_UNPACK (x) + INUM_STEP);
if (SCM_LIKELY (SCM_I_INUMP (result)))
RETURN (result);
@ -328,15 +331,14 @@ VM_DEFINE_FUNCTION (153, sub1, "sub1", 1)
{
ARGS1 (x);
/* Check for underflow. */
if (SCM_LIKELY ((scm_t_intptr) SCM_UNPACK (x) > INUM_MIN))
/* Check for overflow. We must avoid overflow in the signed
subtraction below, even if X is not an inum. */
if (SCM_LIKELY ((scm_t_signed_bits) SCM_UNPACK (x) >= INUM_MIN + INUM_STEP))
{
SCM result;
/* Substract the integers without untagging. */
result = SCM_PACK ((scm_t_intptr) SCM_UNPACK (x)
- (scm_t_intptr) SCM_UNPACK (SCM_I_MAKINUM (1))
+ scm_tc2_int);
/* Substract 1 from the integer without untagging. */
result = SCM_PACK ((scm_t_signed_bits) SCM_UNPACK (x) - INUM_STEP);
if (SCM_LIKELY (SCM_I_INUMP (result)))
RETURN (result);