[Python-checkins] r77453 - in python/branches/release31-maint: Lib/test/floating_points.txt Lib/test/test_float.py Misc/NEWS Python/dtoa.c
mark.dickinson
python-checkins at python.org
Wed Jan 13 00:09:27 CET 2010
Author: mark.dickinson
Date: Wed Jan 13 00:09:26 2010
New Revision: 77453
Log:
Merged revisions 77452 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k
................
r77452 | mark.dickinson | 2010-01-12 23:04:19 +0000 (Tue, 12 Jan 2010) | 23 lines
Merged revisions 77410,77421,77450-77451 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r77410 | mark.dickinson | 2010-01-10 13:06:31 +0000 (Sun, 10 Jan 2010) | 1 line
Remove unused BCinfo fields and an unused macro.
........
r77421 | mark.dickinson | 2010-01-11 17:15:13 +0000 (Mon, 11 Jan 2010) | 1 line
Change a variable type to avoid signed overflow; replace repeated '19999' constant by a define.
........
r77450 | mark.dickinson | 2010-01-12 22:23:56 +0000 (Tue, 12 Jan 2010) | 4 lines
Issue #7632: Fix a problem with _Py_dg_strtod that could lead to
crashes in debug builds, for certain long numeric strings
corresponding to subnormal values.
........
r77451 | mark.dickinson | 2010-01-12 22:55:51 +0000 (Tue, 12 Jan 2010) | 2 lines
Issue #7632: Fix a bug in dtoa.c that could lead to incorrectly-rounded results.
........
................
Modified:
python/branches/release31-maint/ (props changed)
python/branches/release31-maint/Lib/test/floating_points.txt
python/branches/release31-maint/Lib/test/test_float.py
python/branches/release31-maint/Misc/NEWS
python/branches/release31-maint/Python/dtoa.c
Modified: python/branches/release31-maint/Lib/test/floating_points.txt
==============================================================================
--- python/branches/release31-maint/Lib/test/floating_points.txt (original)
+++ python/branches/release31-maint/Lib/test/floating_points.txt Wed Jan 13 00:09:26 2010
@@ -1019,3 +1019,10 @@
+43723334984997307E-26
+10182419849537963E-24
-93501703572661982E-26
+
+# A value that caused a crash in debug builds for Python >= 2.7, 3.1
+# See http://bugs.python.org/issue7632
+2183167012312112312312.23538020374420446192e-370
+
+# Another value designed to test a corner case of Python's strtod code.
+0.99999999999999999999999999999999999999999e+23
Modified: python/branches/release31-maint/Lib/test/test_float.py
==============================================================================
--- python/branches/release31-maint/Lib/test/test_float.py (original)
+++ python/branches/release31-maint/Lib/test/test_float.py Wed Jan 13 00:09:26 2010
@@ -7,6 +7,7 @@
from math import isinf, isnan, copysign, ldexp
import operator
import random, fractions
+import re
INF = float("inf")
NAN = float("nan")
@@ -15,6 +16,74 @@
test_dir = os.path.dirname(__file__) or os.curdir
format_testfile = os.path.join(test_dir, 'formatfloat_testcases.txt')
+finite_decimal_parser = re.compile(r""" # A numeric string consists of:
+ (?P<sign>[-+])? # an optional sign, followed by
+ (?=\d|\.\d) # a number with at least one digit
+ (?P<int>\d*) # having a (possibly empty) integer part
+ (?:\.(?P<frac>\d*))? # followed by an optional fractional part
+ (?:E(?P<exp>[-+]?\d+))? # and an optional exponent
+ \Z
+""", re.VERBOSE | re.IGNORECASE | re.UNICODE).match
+
+# Pure Python version of correctly rounded string->float conversion.
+# Avoids any use of floating-point by returning the result as a hex string.
+def strtod(s, mant_dig=53, min_exp = -1021, max_exp = 1024):
+ """Convert a finite decimal string to a hex string representing an
+ IEEE 754 binary64 float. Return 'inf' or '-inf' on overflow.
+ This function makes no use of floating-point arithmetic at any
+ stage."""
+
+ # parse string into a pair of integers 'a' and 'b' such that
+ # abs(decimal value) = a/b, and a boolean 'negative'.
+ m = finite_decimal_parser(s)
+ if m is None:
+ raise ValueError('invalid numeric string')
+ fraction = m.group('frac') or ''
+ intpart = int(m.group('int') + fraction)
+ exp = int(m.group('exp') or '0') - len(fraction)
+ negative = m.group('sign') == '-'
+ a, b = intpart*10**max(exp, 0), 10**max(0, -exp)
+
+ # quick return for zeros
+ if not a:
+ return '-0x0.0p+0' if negative else '0x0.0p+0'
+
+ # compute exponent e for result; may be one too small in the case
+ # that the rounded value of a/b lies in a different binade from a/b
+ d = a.bit_length() - b.bit_length()
+ d += (a >> d if d >= 0 else a << -d) >= b
+ e = max(d, min_exp) - mant_dig
+
+ # approximate a/b by number of the form q * 2**e; adjust e if necessary
+ a, b = a << max(-e, 0), b << max(e, 0)
+ q, r = divmod(a, b)
+ if 2*r > b or 2*r == b and q & 1:
+ q += 1
+ if q.bit_length() == mant_dig+1:
+ q //= 2
+ e += 1
+
+ # double check that (q, e) has the right form
+ assert q.bit_length() <= mant_dig and e >= min_exp - mant_dig
+ assert q.bit_length() == mant_dig or e == min_exp - mant_dig
+
+ # check for overflow and underflow
+ if e + q.bit_length() > max_exp:
+ return '-inf' if negative else 'inf'
+ if not q:
+ return '-0x0.0p+0' if negative else '0x0.0p+0'
+
+ # for hex representation, shift so # bits after point is a multiple of 4
+ hexdigs = 1 + (mant_dig-2)//4
+ shift = 3 - (mant_dig-2)%4
+ q, e = q << shift, e - shift
+ return '{}0x{:x}.{:0{}x}p{:+d}'.format(
+ '-' if negative else '',
+ q // 16**hexdigs,
+ q % 16**hexdigs,
+ hexdigs,
+ e + 4*hexdigs)
+
class GeneralFloatCases(unittest.TestCase):
def test_float(self):
@@ -1017,6 +1086,38 @@
else:
self.identical(x, fromHex(toHex(x)))
+class StrtodTestCase(unittest.TestCase):
+ def check_string(self, s):
+ expected = strtod(s)
+ try:
+ fs = float(s)
+ except OverflowError:
+ got = '-inf' if s[0] == '-' else 'inf'
+ else:
+ got = fs.hex()
+ self.assertEqual(expected, got,
+ "Incorrectly rounded str->float conversion for "
+ "{}: expected {}, got {}".format(s, expected, got))
+
+ @unittest.skipUnless(getattr(sys, 'float_repr_style', '') == 'short',
+ "applies only when using short float repr style")
+ def test_bug7632(self):
+ # check a few particular values that gave incorrectly rounded
+ # results with previous versions of dtoa.c
+ test_strings = [
+ '94393431193180696942841837085033647913224148539854e-358',
+ '12579816049008305546974391768996369464963024663104e-357',
+ '17489628565202117263145367596028389348922981857013e-357',
+ '18487398785991994634182916638542680759613590482273e-357',
+ '32002864200581033134358724675198044527469366773928e-358',
+ '73608278998966969345824653500136787876436005957953e-358',
+ '64774478836417299491718435234611299336288082136054e-358',
+ '13704940134126574534878641876947980878824688451169e-357',
+ '46697445774047060960624497964425416610480524760471e-358',
+ ]
+ for s in test_strings:
+ self.check_string(s)
+
def test_main():
support.run_unittest(
@@ -1029,6 +1130,7 @@
RoundTestCase,
InfNanTest,
HexFloatTestCase,
+ StrtodTestCase,
)
if __name__ == '__main__':
Modified: python/branches/release31-maint/Misc/NEWS
==============================================================================
--- python/branches/release31-maint/Misc/NEWS (original)
+++ python/branches/release31-maint/Misc/NEWS Wed Jan 13 00:09:26 2010
@@ -12,6 +12,11 @@
Core and Builtins
-----------------
+- Issue #7632: Fix a crash in dtoa.c that occurred in debug builds
+ when parsing certain long numeric strings corresponding to subnormal
+ values. Also fix a number of bugs in dtoa.c that could lead to
+ incorrectly rounded results when converting strings to floats.
+
- Issue #7604: Deleting an unset slotted attribute did not raise an
AttributeError.
Modified: python/branches/release31-maint/Python/dtoa.c
==============================================================================
--- python/branches/release31-maint/Python/dtoa.c (original)
+++ python/branches/release31-maint/Python/dtoa.c Wed Jan 13 00:09:26 2010
@@ -200,10 +200,11 @@
#define STRTOD_DIGLIM 40
#endif
-#ifdef DIGLIM_DEBUG
-extern int strtod_diglim;
-#else
-#define strtod_diglim STRTOD_DIGLIM
+/* maximum permitted exponent value for strtod; exponents larger than
+ MAX_ABS_EXP in absolute value get truncated to +-MAX_ABS_EXP. MAX_ABS_EXP
+ should fit into an int. */
+#ifndef MAX_ABS_EXP
+#define MAX_ABS_EXP 19999U
#endif
/* The following definition of Storeinc is appropriate for MIPS processors.
@@ -269,8 +270,7 @@
typedef struct BCinfo BCinfo;
struct
BCinfo {
- int dp0, dp1, dplen, dsign, e0, inexact;
- int nd, nd0, rounding, scale, uflchk;
+ int dp0, dp1, dplen, dsign, e0, nd, nd0, scale;
};
#define FFFFFFFF 0xffffffffUL
@@ -1130,6 +1130,26 @@
return q;
}
+/* version of ulp(x) that takes bc.scale into account.
+
+ Assuming that x is finite and nonzero, and x / 2^bc.scale is exactly
+ representable as a double, sulp(x) is equivalent to 2^bc.scale * ulp(x /
+ 2^bc.scale). */
+
+static double
+sulp(U *x, BCinfo *bc)
+{
+ U u;
+
+ if (bc->scale && 2*P + 1 - ((word0(x) & Exp_mask) >> Exp_shift) > 0) {
+ /* rv/2^bc->scale is subnormal */
+ word0(&u) = (P+2)*Exp_msk1;
+ word1(&u) = 0;
+ return u.d;
+ }
+ else
+ return ulp(x);
+}
/* return 0 on success, -1 on failure */
@@ -1142,7 +1162,7 @@
dsign = bc->dsign;
nd = bc->nd;
nd0 = bc->nd0;
- p5 = nd + bc->e0 - 1;
+ p5 = nd + bc->e0;
speccase = 0;
if (rv->d == 0.) { /* special case: value near underflow-to-zero */
/* threshold was rounded to zero */
@@ -1227,17 +1247,21 @@
}
}
- /* Now b/d = exactly half-way between the two floating-point values */
- /* on either side of the input string. Compute first digit of b/d. */
-
- if (!(dig = quorem(b,d))) {
- b = multadd(b, 10, 0); /* very unlikely */
- if (b == NULL) {
- Bfree(d);
- return -1;
- }
- dig = quorem(b,d);
+ /* Now 10*b/d = exactly half-way between the two floating-point values
+ on either side of the input string. If b >= d, round down. */
+ if (cmp(b, d) >= 0) {
+ dd = -1;
+ goto ret;
}
+
+ /* Compute first digit of 10*b/d. */
+ b = multadd(b, 10, 0);
+ if (b == NULL) {
+ Bfree(d);
+ return -1;
+ }
+ dig = quorem(b, d);
+ assert(dig < 10);
/* Compare b/d with s0 */
@@ -1285,12 +1309,12 @@
else if (dd < 0) {
if (!dsign) /* does not happen for round-near */
retlow1:
- dval(rv) -= ulp(rv);
+ dval(rv) -= sulp(rv, bc);
}
else if (dd > 0) {
if (dsign) {
rethi1:
- dval(rv) += ulp(rv);
+ dval(rv) += sulp(rv, bc);
}
}
else {
@@ -1312,13 +1336,12 @@
int esign, i, j, k, nd, nd0, nf, nz, nz0, sign;
const char *s, *s0, *s1;
double aadj, aadj1;
- Long L;
U aadj2, adj, rv, rv0;
- ULong y, z;
+ ULong y, z, L;
BCinfo bc;
Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
- sign = nz0 = nz = bc.dplen = bc.uflchk = 0;
+ sign = nz0 = nz = bc.dplen = 0;
dval(&rv) = 0.;
for(s = s00;;s++) switch(*s) {
case '-':
@@ -1413,11 +1436,11 @@
s1 = s;
while((c = *++s) >= '0' && c <= '9')
L = 10*L + c - '0';
- if (s - s1 > 8 || L > 19999)
+ if (s - s1 > 8 || L > MAX_ABS_EXP)
/* Avoid confusion from exponents
* so large that e might overflow.
*/
- e = 19999; /* safe for 16 bit ints */
+ e = (int)MAX_ABS_EXP; /* safe for 16 bit ints */
else
e = (int)L;
if (esign)
@@ -1555,11 +1578,11 @@
/* Put digits into bd: true value = bd * 10^e */
bc.nd = nd;
- bc.nd0 = nd0; /* Only needed if nd > strtod_diglim, but done here */
+ bc.nd0 = nd0; /* Only needed if nd > STRTOD_DIGLIM, but done here */
/* to silence an erroneous warning about bc.nd0 */
/* possibly not being initialized. */
- if (nd > strtod_diglim) {
- /* ASSERT(strtod_diglim >= 18); 18 == one more than the */
+ if (nd > STRTOD_DIGLIM) {
+ /* ASSERT(STRTOD_DIGLIM >= 18); 18 == one more than the */
/* minimum number of decimal digits to distinguish double values */
/* in IEEE arithmetic. */
i = j = 18;
@@ -1767,10 +1790,8 @@
/* accept rv */
break;
/* rv = smallest denormal */
- if (bc.nd >nd) {
- bc.uflchk = 1;
+ if (bc.nd >nd)
break;
- }
goto undfl;
}
}
@@ -1786,10 +1807,8 @@
else {
dval(&rv) -= ulp(&rv);
if (!dval(&rv)) {
- if (bc.nd >nd) {
- bc.uflchk = 1;
+ if (bc.nd >nd)
break;
- }
goto undfl;
}
}
@@ -1801,10 +1820,8 @@
aadj = aadj1 = 1.;
else if (word1(&rv) || word0(&rv) & Bndry_mask) {
if (word1(&rv) == Tiny1 && !word0(&rv)) {
- if (bc.nd >nd) {
- bc.uflchk = 1;
+ if (bc.nd >nd)
break;
- }
goto undfl;
}
aadj = 1.;
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