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........
  r77519 | mark.dickinson | 2010-01-16 10:44:00 +0000 (Sat, 16 Jan 2010) | 5 lines

  Issue #7632: Fix a serious wrong output bug for string -> float conversion.
  Also remove some now unused variables, and add comments clarifying the
  possible outputs of the parsing section of _Py_dg_strtod.  Thanks
  Eric Smith for reviewing.
........
  r77530 | mark.dickinson | 2010-01-16 17:57:49 +0000 (Sat, 16 Jan 2010) | 3 lines

  Issue #7632: Fix one more case of incorrect rounding for str -> float
  conversion (see bug 5 in the issue tracker).
........
  r77533 | mark.dickinson | 2010-01-16 18:06:17 +0000 (Sat, 16 Jan 2010) | 1 line

  Fix multiple uses of variable 'L' in _Py_dg_strtod, where one use requires an unsigned long and the other a signed long.  See also r77421.
........
This commit is contained in:
Mark Dickinson 2010-01-16 18:10:25 +00:00
parent 747e8b3f58
commit 45b6365974
3 changed files with 100 additions and 47 deletions
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11
Lib/test/test_strtod.py
View File

@ -123,10 +123,6 @@ class StrtodTests(unittest.TestCase):
digits = m * 5**-e
exponent = e
s = '{}e{}'.format(digits, exponent)
# for the moment, ignore errors from trailing zeros
if digits % 10 == 0:
continue
self.check_strtod(s)
# get expected answer via struct, to triple check
@ -175,7 +171,8 @@ class StrtodTests(unittest.TestCase):
self.check_strtod(s)
def test_parsing(self):
digits = tuple(map(str, range(10)))
# make '0' more likely to be chosen than other digits
digits = '000000123456789'
signs = ('+', '-', '')
# put together random short valid strings
@ -257,7 +254,9 @@ class StrtodTests(unittest.TestCase):
'247032822920623295e-341',
# issue 7632 bug 5: the following 2 strings convert differently
'1000000000000000000000000000000000000000e-16',
#'10000000000000000000000000000000000000000e-17',
'10000000000000000000000000000000000000000e-17',
# issue 7632 bug 8: the following produced 10.0
'10.900000000000000012345678912345678912345',
]
for s in test_strings:
self.check_strtod(s)

10
Misc/NEWS
View File

@ -16,10 +16,12 @@ Core and Builtins
methods of bytes, bytearray and unicode objects by using a common
implementation based on stringlib's fast search. Patch by Florent Xicluna.
- 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 #7632: Fix various str -> float conversion bugs present in 2.7
alpha 2, including: (1) a serious 'wrong output' bug that could
occur for long (> 40 digit) input strings, (2) a crash in dtoa.c
that occurred in debug builds when parsing certain long numeric
strings corresponding to subnormal values, and (3) a number of flaws
that could lead to incorrectly rounded results.
- The __complex__ method is now looked up on the class of instances to make it
consistent with other special methods.

126
Python/dtoa.c
View File

@ -1340,16 +1340,17 @@ bigcomp(U *rv, const char *s0, BCinfo *bc)
double
_Py_dg_strtod(const char *s00, char **se)
{
int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, dp0, dp1, dplen, e, e1, error;
int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, e, e1, error;
int esign, i, j, k, nd, nd0, nf, nz, nz0, sign;
const char *s, *s0, *s1;
double aadj, aadj1;
U aadj2, adj, rv, rv0;
ULong y, z, L;
ULong y, z, abse;
Long L;
BCinfo bc;
Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
sign = nz0 = nz = dplen = 0;
sign = nz0 = nz = 0;
dval(&rv) = 0.;
for(s = s00;;s++) switch(*s) {
case '-':
@ -1381,18 +1382,11 @@ _Py_dg_strtod(const char *s00, char **se)
goto ret;
}
s0 = s;
y = z = 0;
for(nd = nf = 0; (c = *s) >= '0' && c <= '9'; nd++, s++)
if (nd < 9)
y = 10*y + c - '0';
else if (nd < 16)
z = 10*z + c - '0';
;
nd0 = nd;
dp0 = dp1 = s - s0;
if (c == '.') {
c = *++s;
dp1 = s - s0;
dplen = 1;
if (!nd) {
for(; c == '0'; c = *++s)
nz++;
@ -1409,15 +1403,7 @@ _Py_dg_strtod(const char *s00, char **se)
nz++;
if (c -= '0') {
nf += nz;
for(i = 1; i < nz; i++)
if (nd++ < 9)
y *= 10;
else if (nd <= DBL_DIG + 1)
z *= 10;
if (nd++ < 9)
y = 10*y + c;
else if (nd <= DBL_DIG + 1)
z = 10*z + c;
nd += nz;
nz = 0;
}
}
@ -1440,17 +1426,17 @@ _Py_dg_strtod(const char *s00, char **se)
while(c == '0')
c = *++s;
if (c > '0' && c <= '9') {
L = c - '0';
abse = c - '0';
s1 = s;
while((c = *++s) >= '0' && c <= '9')
L = 10*L + c - '0';
if (s - s1 > 8 || L > MAX_ABS_EXP)
abse = 10*abse + c - '0';
if (s - s1 > 8 || abse > MAX_ABS_EXP)
/* Avoid confusion from exponents
* so large that e might overflow.
*/
e = (int)MAX_ABS_EXP; /* safe for 16 bit ints */
else
e = (int)L;
e = (int)abse;
if (esign)
e = -e;
}
@ -1468,15 +1454,78 @@ _Py_dg_strtod(const char *s00, char **se)
}
goto ret;
}
bc.e0 = e1 = e -= nf;
e -= nf;
if (!nd0)
nd0 = nd;
/* strip trailing zeros */
for (i = nd; i > 0; ) {
/* scan back until we hit a nonzero digit. significant digit 'i'
is s0[i] if i < nd0, s0[i+1] if i >= nd0. */
--i;
if (s0[i < nd0 ? i : i+1] != '0') {
++i;
break;
}
}
e += nd - i;
nd = i;
if (nd0 > nd)
nd0 = nd;
/* Now we have nd0 digits, starting at s0, followed by a
* decimal point, followed by nd-nd0 digits. The number we're
* after is the integer represented by those digits times
* 10**e */
if (!nd0)
nd0 = nd;
bc.e0 = e1 = e;
/* Summary of parsing results. The parsing stage gives values
* s0, nd0, nd, e, sign, where:
*
* - s0 points to the first significant digit of the input string s00;
*
* - nd is the total number of significant digits (here, and
* below, 'significant digits' means the set of digits of the
* significand of the input that remain after ignoring leading
* and trailing zeros.
*
* - nd0 indicates the position of the decimal point (if
* present): so the nd significant digits are in s0[0:nd0] and
* s0[nd0+1:nd+1] using the usual Python half-open slice
* notation. (If nd0 < nd, then s0[nd0] necessarily contains
* a '.' character; if nd0 == nd, then it could be anything.)
*
* - e is the adjusted exponent: the absolute value of the number
* represented by the original input string is n * 10**e, where
* n is the integer represented by the concatenation of
* s0[0:nd0] and s0[nd0+1:nd+1]
*
* - sign gives the sign of the input: 1 for negative, 0 for positive
*
* - the first and last significant digits are nonzero
*/
/* put first DBL_DIG+1 digits into integer y and z.
*
* - y contains the value represented by the first min(9, nd)
* significant digits
*
* - if nd > 9, z contains the value represented by significant digits
* with indices in [9, min(16, nd)). So y * 10**(min(16, nd) - 9) + z
* gives the value represented by the first min(16, nd) sig. digits.
*/
y = z = 0;
for (i = 0; i < nd; i++) {
if (i < 9)
y = 10*y + s0[i < nd0 ? i : i+1] - '0';
else if (i < DBL_DIG+1)
z = 10*z + s0[i < nd0 ? i : i+1] - '0';
else
break;
}
k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1;
dval(&rv) = y;
if (k > 9) {
@ -1593,15 +1642,18 @@ _Py_dg_strtod(const char *s00, char **se)
/* ASSERT(STRTOD_DIGLIM >= 18); 18 == one more than the */
/* minimum number of decimal digits to distinguish double values */
/* in IEEE arithmetic. */
i = j = 18;
if (i > nd0)
j += dplen;
for(;;) {
if (--j <= dp1 && j >= dp0)
j = dp0 - 1;
if (s0[j] != '0')
break;
/* Truncate input to 18 significant digits, then discard any trailing
zeros on the result by updating nd, nd0, e and y suitably. (There's
no need to update z; it's not reused beyond this point.) */
for (i = 18; i > 0; ) {
/* scan back until we hit a nonzero digit. significant digit 'i'
is s0[i] if i < nd0, s0[i+1] if i >= nd0. */
--i;
if (s0[i < nd0 ? i : i+1] != '0') {
++i;
break;
}
}
e += nd - i;
nd = i;
@ -1611,8 +1663,8 @@ _Py_dg_strtod(const char *s00, char **se)
y = 0;
for(i = 0; i < nd0; ++i)
y = 10*y + s0[i] - '0';
for(j = dp1; i < nd; ++i)
y = 10*y + s0[j++] - '0';
for(; i < nd; ++i)
y = 10*y + s0[i+1] - '0';
}
}
bd0 = s2b(s0, nd0, nd, y);