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Bug #1521947: possible bug in mystrtol.c with recent gcc.

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In general, C doesn't define anything about what happens when
an operation on a signed integral type overflows, and PyOS_strtol()
did several formally undefined things of that nature on signed
longs.  Some version of gcc apparently tries to exploit that now,
and PyOS_strtol() could fail to detect overflow then.

Tried to repair all that, although it seems at least as likely to me
that we'll get screwed by bad platform definitions for LONG_MIN
and/or LONG_MAX now.  For that reason, I don't recommend backporting
this.

Note that I have no box on which this makes a lick of difference --
can't really test it, except to note that it didn't break anything
on my boxes.

Silent change:  PyOS_strtol() used to return the hard-coded 0x7fffffff
in case of overflow.  Now it returns LONG_MAX.  They're the same only on
32-bit boxes (although C doesn't guarantee that either ...).
This commit is contained in:
Tim Peters 2006-07-27 01:14:53 +00:00
parent 95621b25dc
commit bc24eee333
2 changed files with 29 additions and 12 deletions
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32
Python/mystrtoul.c
View file

@ -195,10 +195,19 @@ overflowed:
return (unsigned long)-1;
}
/* Checking for overflow in PyOS_strtol is a PITA since C doesn't define
* anything about what happens when a signed integer operation overflows,
* and some compilers think they're doing you a favor by being "clever"
* then. Python assumes a 2's-complement representation, so that the bit
* pattern for the largest postive signed long is LONG_MAX, and for
* the smallest negative signed long is LONG_MAX + 1.
*/
long
PyOS_strtol(char *str, char **ptr, int base)
{
long result;
unsigned long uresult;
char sign;
while (*str && isspace(Py_CHARMASK(*str)))
@ -208,17 +217,20 @@ PyOS_strtol(char *str, char **ptr, int base)
if (sign == '+' || sign == '-')
str++;
result = (long) PyOS_strtoul(str, ptr, base);
uresult = PyOS_strtoul(str, ptr, base);
/* Signal overflow if the result appears negative,
except for the largest negative integer */
if (result < 0 && !(sign == '-' && result == -result)) {
errno = ERANGE;
result = 0x7fffffff;
if (uresult <= (unsigned long)LONG_MAX) {
result = (long)uresult;
if (sign == '-')
result = -result;
}
else if (sign == '-' && uresult == (unsigned long)LONG_MAX + 1) {
assert(LONG_MIN == -LONG_MAX-1);
result = LONG_MIN;
}
else {
errno = ERANGE;
result = LONG_MAX;
}
if (sign == '-')
result = -result;
return result;
}