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Patch for bug #659709: bogus computation of float length

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Python 2.2.x backport candidate. (This bug has been around since
Python 1.6.)
This commit is contained in:
Marc-André Lemburg 2002-12-29 19:44:06 +00:00
parent bbfb910416
commit 79f57833f3
4 changed files with 88 additions and 16 deletions
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26
Lib/test/test_string.py
View file

@ -57,3 +57,29 @@ def __repr__(self):
string.whitespace
string.lowercase
string.uppercase
# Float formatting
for prec in range(100):
formatstring = u'%%.%if' % prec
value = 0.01
for x in range(60):
value = value * 3.141592655 / 3.0 * 10.0
#print 'Overflow check for x=%i and prec=%i:' % \
# (x, prec),
try:
result = formatstring % value
except OverflowError:
# The formatfloat() code in stringobject.c and
# unicodeobject.c uses a 120 byte buffer and switches from
# 'f' formatting to 'g' at precision 50, so we expect
# OverflowErrors for the ranges x < 50 and prec >= 67.
if x >= 50 or \
prec < 67:
print '*** unexpected OverflowError for x=%i and prec=%i' % (x, prec)
else:
#print 'OverflowError'
pass
else:
#print result
pass

25
Lib/test/test_unicode.py
View file

@ -476,6 +476,31 @@ def test_fixup(s):
else:
print '*** formatting u"%%c" %% %i should give a ValueError' % ordinal
# float formatting
for prec in range(100):
formatstring = u'%%.%if' % prec
value = 0.01
for x in range(60):
value = value * 3.141592655 / 3.0 * 10.0
#print 'Overflow check for x=%i and prec=%i:' % \
# (x, prec),
try:
result = formatstring % value
except OverflowError:
# The formatfloat() code in stringobject.c and
# unicodeobject.c uses a 120 byte buffer and switches from
# 'f' formatting to 'g' at precision 50, so we expect
# OverflowErrors for the ranges x < 50 and prec >= 67.
if x >= 50 or \
prec < 67:
print '*** unexpected OverflowError for x=%i and prec=%i' % (x, prec)
else:
#print 'OverflowError'
pass
else:
#print result
pass
# formatting jobs delegated from the string implementation:
verify('...%(foo)s...' % {'foo':u"abc"} == u'...abc...')
verify('...%(foo)s...' % {'foo':"abc"} == '...abc...')

22
Objects/stringobject.c
View file

@ -3361,21 +3361,31 @@ formatfloat(char *buf, size_t buflen, int flags,
prec = 6;
if (type == 'f' && fabs(x)/1e25 >= 1e25)
type = 'g';
PyOS_snprintf(fmt, sizeof(fmt), "%%%s.%d%c",
(flags&F_ALT) ? "#" : "",
prec, type);
/* worst case length calc to ensure no buffer overrun:
/* Worst case length calc to ensure no buffer overrun:
'g' formats:
fmt = %#.<prec>g
buf = '-' + [0-9]*prec + '.' + 'e+' + (longest exp
for any double rep.)
len = 1 + prec + 1 + 2 + 5 = 9 + prec
'f' formats:
buf = '-' + [0-9]*x + '.' + [0-9]*prec (with x < 50)
len = 1 + 50 + 1 + prec = 52 + prec
If prec=0 the effective precision is 1 (the leading digit is
always given), therefore increase by one to 10+prec. */
if (buflen <= (size_t)10 + (size_t)prec) {
always given), therefore increase the length by one.
*/
if ((type == 'g' && buflen <= (size_t)10 + (size_t)prec) ||
(type == 'f' && buflen <= (size_t)53 + (size_t)prec)) {
PyErr_SetString(PyExc_OverflowError,
"formatted float is too long (precision too large?)");
return -1;
}
PyOS_snprintf(fmt, sizeof(fmt), "%%%s.%d%c",
(flags&F_ALT) ? "#" : "",
prec, type);
PyOS_snprintf(buf, buflen, fmt, x);
return strlen(buf);
}

31
Objects/unicodeobject.c
View file

@ -5999,20 +5999,31 @@ formatfloat(Py_UNICODE *buf,
prec = 6;
if (type == 'f' && (fabs(x) / 1e25) >= 1e25)
type = 'g';
PyOS_snprintf(fmt, sizeof(fmt), "%%%s.%d%c",
(flags & F_ALT) ? "#" : "", prec, type);
/* worst case length calc to ensure no buffer overrun:
fmt = %#.<prec>g
buf = '-' + [0-9]*prec + '.' + 'e+' + (longest exp
for any double rep.)
len = 1 + prec + 1 + 2 + 5 = 9 + prec
/* Worst case length calc to ensure no buffer overrun:
'g' formats:
fmt = %#.<prec>g
buf = '-' + [0-9]*prec + '.' + 'e+' + (longest exp
for any double rep.)
len = 1 + prec + 1 + 2 + 5 = 9 + prec
'f' formats:
buf = '-' + [0-9]*x + '.' + [0-9]*prec (with x < 50)
len = 1 + 50 + 1 + prec = 52 + prec
If prec=0 the effective precision is 1 (the leading digit is
always given), therefore increase by one to 10+prec. */
if (buflen <= (size_t)10 + (size_t)prec) {
always given), therefore increase the length by one.
*/
if ((type == 'g' && buflen <= (size_t)10 + (size_t)prec) ||
(type == 'f' && buflen <= (size_t)53 + (size_t)prec)) {
PyErr_SetString(PyExc_OverflowError,
"formatted float is too long (precision too long?)");
"formatted float is too long (precision too large?)");
return -1;
}
PyOS_snprintf(fmt, sizeof(fmt), "%%%s.%d%c",
(flags&F_ALT) ? "#" : "",
prec, type);
return usprintf(buf, fmt, x);
}