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. ........
This commit is contained in:
Mark Dickinson
parent
f845302d06
commit
81612e8778
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@ -1019,3 +1019,10 @@
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+43723334984997307E-26
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+10182419849537963E-24
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-93501703572661982E-26
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# A value that caused a crash in debug builds for Python >= 2.7, 3.1
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# See http://bugs.python.org/issue7632
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2183167012312112312312.23538020374420446192e-370
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# Another value designed to test a corner case of Python's strtod code.
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0.99999999999999999999999999999999999999999e+23
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@ -7,6 +7,7 @@ import math
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from math import isinf, isnan, copysign, ldexp
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import operator
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import random, fractions
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import re
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INF = float("inf")
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NAN = float("nan")
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@ -20,6 +21,74 @@ requires_IEEE_754 = unittest.skipUnless(
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test_dir = os.path.dirname(__file__) or os.curdir
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format_testfile = os.path.join(test_dir, 'formatfloat_testcases.txt')
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finite_decimal_parser = re.compile(r""" # A numeric string consists of:
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(?P<sign>[-+])? # an optional sign, followed by
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(?=\d|\.\d) # a number with at least one digit
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(?P<int>\d*) # having a (possibly empty) integer part
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(?:\.(?P<frac>\d*))? # followed by an optional fractional part
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(?:E(?P<exp>[-+]?\d+))? # and an optional exponent
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\Z
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""", re.VERBOSE | re.IGNORECASE | re.UNICODE).match
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# Pure Python version of correctly rounded string->float conversion.
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# Avoids any use of floating-point by returning the result as a hex string.
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def strtod(s, mant_dig=53, min_exp = -1021, max_exp = 1024):
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"""Convert a finite decimal string to a hex string representing an
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IEEE 754 binary64 float. Return 'inf' or '-inf' on overflow.
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This function makes no use of floating-point arithmetic at any
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stage."""
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# parse string into a pair of integers 'a' and 'b' such that
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# abs(decimal value) = a/b, and a boolean 'negative'.
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m = finite_decimal_parser(s)
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if m is None:
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raise ValueError('invalid numeric string')
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fraction = m.group('frac') or ''
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intpart = int(m.group('int') + fraction)
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exp = int(m.group('exp') or '0') - len(fraction)
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negative = m.group('sign') == '-'
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a, b = intpart*10**max(exp, 0), 10**max(0, -exp)
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# quick return for zeros
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if not a:
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return '-0x0.0p+0' if negative else '0x0.0p+0'
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# compute exponent e for result; may be one too small in the case
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# that the rounded value of a/b lies in a different binade from a/b
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d = a.bit_length() - b.bit_length()
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d += (a >> d if d >= 0 else a << -d) >= b
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e = max(d, min_exp) - mant_dig
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# approximate a/b by number of the form q * 2**e; adjust e if necessary
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a, b = a << max(-e, 0), b << max(e, 0)
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q, r = divmod(a, b)
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if 2*r > b or 2*r == b and q & 1:
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q += 1
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if q.bit_length() == mant_dig+1:
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q //= 2
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e += 1
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# double check that (q, e) has the right form
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assert q.bit_length() <= mant_dig and e >= min_exp - mant_dig
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assert q.bit_length() == mant_dig or e == min_exp - mant_dig
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# check for overflow and underflow
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if e + q.bit_length() > max_exp:
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return '-inf' if negative else 'inf'
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if not q:
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return '-0x0.0p+0' if negative else '0x0.0p+0'
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# for hex representation, shift so # bits after point is a multiple of 4
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hexdigs = 1 + (mant_dig-2)//4
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shift = 3 - (mant_dig-2)%4
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q, e = q << shift, e - shift
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return '{}0x{:x}.{:0{}x}p{:+d}'.format(
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'-' if negative else '',
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q // 16**hexdigs,
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q % 16**hexdigs,
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hexdigs,
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e + 4*hexdigs)
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class GeneralFloatCases(unittest.TestCase):
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def test_float(self):
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@ -1263,6 +1332,38 @@ class HexFloatTestCase(unittest.TestCase):
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else:
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self.identical(x, fromHex(toHex(x)))
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class StrtodTestCase(unittest.TestCase):
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def check_string(self, s):
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expected = strtod(s)
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try:
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fs = float(s)
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except OverflowError:
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got = '-inf' if s[0] == '-' else 'inf'
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else:
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got = fs.hex()
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self.assertEqual(expected, got,
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"Incorrectly rounded str->float conversion for "
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"{}: expected {}, got {}".format(s, expected, got))
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@unittest.skipUnless(getattr(sys, 'float_repr_style', '') == 'short',
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"applies only when using short float repr style")
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def test_bug7632(self):
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# check a few particular values that gave incorrectly rounded
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# results with previous versions of dtoa.c
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test_strings = [
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'94393431193180696942841837085033647913224148539854e-358',
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'12579816049008305546974391768996369464963024663104e-357',
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'17489628565202117263145367596028389348922981857013e-357',
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'18487398785991994634182916638542680759613590482273e-357',
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'32002864200581033134358724675198044527469366773928e-358',
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'73608278998966969345824653500136787876436005957953e-358',
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'64774478836417299491718435234611299336288082136054e-358',
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'13704940134126574534878641876947980878824688451169e-357',
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'46697445774047060960624497964425416610480524760471e-358',
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]
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for s in test_strings:
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self.check_string(s)
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def test_main():
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support.run_unittest(
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@ -1275,6 +1376,7 @@ def test_main():
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RoundTestCase,
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InfNanTest,
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HexFloatTestCase,
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StrtodTestCase,
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)
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if __name__ == '__main__':
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@ -12,6 +12,11 @@ What's New in Python 3.2 Alpha 1?
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Core and Builtins
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-----------------
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- Issue #7632: Fix a crash in dtoa.c that occurred in debug builds
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when parsing certain long numeric strings corresponding to subnormal
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values. Also fix a number of bugs in dtoa.c that could lead to
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incorrectly rounded results when converting strings to floats.
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- The __complex__ method is now looked up on the class of instances to make it
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consistent with other special methods.
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@ -200,10 +200,11 @@ typedef union { double d; ULong L[2]; } U;
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#define STRTOD_DIGLIM 40
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#endif
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#ifdef DIGLIM_DEBUG
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extern int strtod_diglim;
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#else
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#define strtod_diglim STRTOD_DIGLIM
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/* maximum permitted exponent value for strtod; exponents larger than
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MAX_ABS_EXP in absolute value get truncated to +-MAX_ABS_EXP. MAX_ABS_EXP
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should fit into an int. */
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#ifndef MAX_ABS_EXP
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#define MAX_ABS_EXP 19999U
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#endif
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/* The following definition of Storeinc is appropriate for MIPS processors.
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@ -269,8 +270,7 @@ extern int strtod_diglim;
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typedef struct BCinfo BCinfo;
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struct
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BCinfo {
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int dp0, dp1, dplen, dsign, e0, inexact;
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int nd, nd0, rounding, scale, uflchk;
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int dp0, dp1, dplen, dsign, e0, nd, nd0, scale;
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};
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#define FFFFFFFF 0xffffffffUL
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@ -1130,6 +1130,26 @@ quorem(Bigint *b, Bigint *S)
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return q;
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}
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/* version of ulp(x) that takes bc.scale into account.
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Assuming that x is finite and nonzero, and x / 2^bc.scale is exactly
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representable as a double, sulp(x) is equivalent to 2^bc.scale * ulp(x /
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2^bc.scale). */
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static double
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sulp(U *x, BCinfo *bc)
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{
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U u;
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if (bc->scale && 2*P + 1 - ((word0(x) & Exp_mask) >> Exp_shift) > 0) {
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/* rv/2^bc->scale is subnormal */
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word0(&u) = (P+2)*Exp_msk1;
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word1(&u) = 0;
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return u.d;
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}
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else
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return ulp(x);
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}
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/* return 0 on success, -1 on failure */
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@ -1142,7 +1162,7 @@ bigcomp(U *rv, const char *s0, BCinfo *bc)
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dsign = bc->dsign;
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nd = bc->nd;
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nd0 = bc->nd0;
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p5 = nd + bc->e0 - 1;
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p5 = nd + bc->e0;
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speccase = 0;
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if (rv->d == 0.) { /* special case: value near underflow-to-zero */
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/* threshold was rounded to zero */
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@ -1227,17 +1247,21 @@ bigcomp(U *rv, const char *s0, BCinfo *bc)
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}
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}
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/* Now b/d = exactly half-way between the two floating-point values */
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/* on either side of the input string. Compute first digit of b/d. */
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if (!(dig = quorem(b,d))) {
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b = multadd(b, 10, 0); /* very unlikely */
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if (b == NULL) {
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Bfree(d);
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return -1;
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}
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dig = quorem(b,d);
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/* Now 10*b/d = exactly half-way between the two floating-point values
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on either side of the input string. If b >= d, round down. */
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if (cmp(b, d) >= 0) {
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dd = -1;
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goto ret;
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}
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/* Compute first digit of 10*b/d. */
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b = multadd(b, 10, 0);
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if (b == NULL) {
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Bfree(d);
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return -1;
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}
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dig = quorem(b, d);
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assert(dig < 10);
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/* Compare b/d with s0 */
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@ -1285,12 +1309,12 @@ bigcomp(U *rv, const char *s0, BCinfo *bc)
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else if (dd < 0) {
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if (!dsign) /* does not happen for round-near */
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retlow1:
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dval(rv) -= ulp(rv);
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dval(rv) -= sulp(rv, bc);
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}
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else if (dd > 0) {
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if (dsign) {
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rethi1:
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dval(rv) += ulp(rv);
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dval(rv) += sulp(rv, bc);
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}
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}
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else {
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@ -1312,13 +1336,12 @@ _Py_dg_strtod(const char *s00, char **se)
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int esign, i, j, k, nd, nd0, nf, nz, nz0, sign;
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const char *s, *s0, *s1;
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double aadj, aadj1;
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Long L;
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U aadj2, adj, rv, rv0;
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ULong y, z;
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ULong y, z, L;
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BCinfo bc;
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Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
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sign = nz0 = nz = bc.dplen = bc.uflchk = 0;
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sign = nz0 = nz = bc.dplen = 0;
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dval(&rv) = 0.;
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for(s = s00;;s++) switch(*s) {
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case '-':
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@ -1413,11 +1436,11 @@ _Py_dg_strtod(const char *s00, char **se)
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s1 = s;
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while((c = *++s) >= '0' && c <= '9')
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L = 10*L + c - '0';
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if (s - s1 > 8 || L > 19999)
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if (s - s1 > 8 || L > MAX_ABS_EXP)
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/* Avoid confusion from exponents
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* so large that e might overflow.
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*/
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e = 19999; /* safe for 16 bit ints */
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e = (int)MAX_ABS_EXP; /* safe for 16 bit ints */
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else
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e = (int)L;
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if (esign)
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@ -1555,11 +1578,11 @@ _Py_dg_strtod(const char *s00, char **se)
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/* Put digits into bd: true value = bd * 10^e */
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bc.nd = nd;
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bc.nd0 = nd0; /* Only needed if nd > strtod_diglim, but done here */
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bc.nd0 = nd0; /* Only needed if nd > STRTOD_DIGLIM, but done here */
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/* to silence an erroneous warning about bc.nd0 */
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/* possibly not being initialized. */
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if (nd > strtod_diglim) {
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/* ASSERT(strtod_diglim >= 18); 18 == one more than the */
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if (nd > STRTOD_DIGLIM) {
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/* ASSERT(STRTOD_DIGLIM >= 18); 18 == one more than the */
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/* minimum number of decimal digits to distinguish double values */
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/* in IEEE arithmetic. */
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i = j = 18;
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@ -1767,10 +1790,8 @@ _Py_dg_strtod(const char *s00, char **se)
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/* accept rv */
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break;
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/* rv = smallest denormal */
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if (bc.nd >nd) {
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bc.uflchk = 1;
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if (bc.nd >nd)
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break;
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}
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goto undfl;
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}
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}
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@ -1786,10 +1807,8 @@ _Py_dg_strtod(const char *s00, char **se)
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else {
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dval(&rv) -= ulp(&rv);
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if (!dval(&rv)) {
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if (bc.nd >nd) {
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bc.uflchk = 1;
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if (bc.nd >nd)
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break;
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}
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goto undfl;
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}
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}
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@ -1801,10 +1820,8 @@ _Py_dg_strtod(const char *s00, char **se)
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aadj = aadj1 = 1.;
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else if (word1(&rv) || word0(&rv) & Bndry_mask) {
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if (word1(&rv) == Tiny1 && !word0(&rv)) {
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if (bc.nd >nd) {
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bc.uflchk = 1;
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if (bc.nd >nd)
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break;
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}
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goto undfl;
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}
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aadj = 1.;
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