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

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* libguile/vm-engine.c (INUM_MIN, INUM_MAX): Redefine without making
  assumptions about the representation.
  (INUM_STEP): New macro.
  (add1, sub1): Avoid signed overflows, and use INUM_STEP.
This commit is contained in:
Mark H Weaver 2013-08-06 17:00:23 -04:00
parent 0bd659658b
commit d2295ba571
1 changed files with 18 additions and 14 deletions
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32
libguile/vm-engine.c
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@ -490,6 +490,7 @@ VM_NAME (SCM vm, SCM program, SCM *argv, int nargs)
#undef INIT
#undef INUM_MAX
#undef INUM_MIN
#undef INUM_STEP
#undef jump_table
#undef LOCAL_REF
#undef LOCAL_SET
@ -754,8 +755,13 @@ VM_NAME (SCM vm, SCM program, SCM *argv, int nargs)
do { LOCAL_SET (dst, x); NEXT (1); } while (0)
/* The maximum/minimum tagged integers. */
#define INUM_MAX (INTPTR_MAX - 1)
#define INUM_MIN (INTPTR_MIN + scm_tc2_int)
#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))
#define BINARY_INTEGER_OP(CFUNC,SFUNC) \
{ \
@ -2807,15 +2813,14 @@ RTL_VM_NAME (SCM vm, SCM program, SCM *argv, size_t nargs_)
{
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);
@ -2842,15 +2847,14 @@ RTL_VM_NAME (SCM vm, SCM program, SCM *argv, size_t nargs_)
{
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);