[Python-checkins] r64974 - in python/trunk: Doc/library/stdtypes.rst Doc/whatsnew/2.6.rst Lib/test/test_float.py Misc/NEWS Objects/floatobject.c
mark.dickinson
python-checkins at python.org
Tue Jul 15 21:08:33 CEST 2008
Author: mark.dickinson
Date: Tue Jul 15 21:08:33 2008
New Revision: 64974
Log:
Issue #3008: add instance method float.hex and class method float.fromhex
to convert floats to and from hexadecimal strings respectively.
Modified:
python/trunk/Doc/library/stdtypes.rst
python/trunk/Doc/whatsnew/2.6.rst
python/trunk/Lib/test/test_float.py
python/trunk/Misc/NEWS
python/trunk/Objects/floatobject.c
Modified: python/trunk/Doc/library/stdtypes.rst
==============================================================================
--- python/trunk/Doc/library/stdtypes.rst (original)
+++ python/trunk/Doc/library/stdtypes.rst Tue Jul 15 21:08:33 2008
@@ -448,6 +448,75 @@
.. _typeiter:
+
+Additional Methods on Float
+---------------------------
+
+The float type has some additional methods to support conversion to
+and from hexadecimal strings. Since Python's floats are stored
+internally as binary numbers, converting a float to or from a
+*decimal* string usually involves a small rounding error. In
+contrast, hexadecimal strings allow exact representation and
+specification of floating-point numbers. This can be useful when
+debugging, and in numerical work.
+
+
+.. method:: float.hex()
+
+ Return a representation of a floating-point number as a hexadecimal
+ string. For finite floating-point numbers, this representation
+ will always include a leading ``0x`` and a trailing ``p`` and
+ exponent.
+
+ .. versionadded:: 2.6
+
+
+.. method:: float.fromhex(s)
+
+ Class method to return the float represented by a hexadecimal
+ string *s*. The string *s* may have leading and trailing
+ whitespace.
+
+ .. versionadded:: 2.6
+
+
+Note that :meth:`float.hex` is an instance method, while
+:meth:`float.fromhex` is a class method.
+
+A hexadecimal string takes the form::
+
+ [sign] ['0x'] integer ['.' fraction] ['p' exponent]
+
+where the optional ``sign`` may by either ``+`` or ``-``, ``integer``
+and ``fraction`` are strings of hexadecimal digits, and ``exponent``
+is a decimal integer with an optional leading sign. Case is not
+significant, and there must be at least one hexadecimal digit in
+either the integer or the fraction. This syntax is similar to the
+syntax specified in section 6.4.4.2 of the C99 standard, and also to
+the syntax used in Java 1.5 onwards. In particular, the output of
+:meth:`float.hex` is usable as a hexadecimal floating-point literal in
+C or Java code, and hexadecimal strings produced by C's ``%a`` format
+character or Java's ``Double.toHexString`` are accepted by
+:meth:`float.fromhex`.
+
+
+Note that the exponent is written in decimal rather than hexadecimal,
+and that it gives the power of 2 by which to multiply the coefficient.
+For example, the hexadecimal string ``0x3.a7p10`` represents the
+floating-point number ``(3 + 10./16 + 7./16**2) * 2.0**10``, or
+``3740.0``::
+
+ >>> float.fromhex('0x3.a7p10')
+ 3740.0
+
+
+Applying the reverse conversion to ``3740.0`` gives a different
+hexadecimal string representing the same number::
+
+ >>> float.hex(3740.0)
+ '0x1.d380000000000p+11'
+
+
Iterator Types
==============
Modified: python/trunk/Doc/whatsnew/2.6.rst
==============================================================================
--- python/trunk/Doc/whatsnew/2.6.rst (original)
+++ python/trunk/Doc/whatsnew/2.6.rst Tue Jul 15 21:08:33 2008
@@ -1521,6 +1521,11 @@
:func:`isnan`, return true if their floating-point argument is
infinite or Not A Number. (:issue:`1640`)
+ The float type has a new instance method :meth:`float.hex` and a
+ corresponding new class method :meth:`float.fromhex` to convert
+ floating-point numbers to and from hexadecimal strings,
+ respectively. (:issue:`3008`)
+
* The :mod:`math` module has a number of new functions, and the existing
functions have been improved to give more consistent behaviour
across platforms, especially with respect to handling of
Modified: python/trunk/Lib/test/test_float.py
==============================================================================
--- python/trunk/Lib/test/test_float.py (original)
+++ python/trunk/Lib/test/test_float.py Tue Jul 15 21:08:33 2008
@@ -3,7 +3,7 @@
import os
from test import test_support
import math
-from math import isinf, isnan
+from math import isinf, isnan, copysign, ldexp
import operator
INF = float("inf")
@@ -343,6 +343,390 @@
self.failIf(NAN.is_inf())
self.failIf((0.).is_inf())
+fromHex = float.fromhex
+toHex = float.hex
+class HexFloatTestCase(unittest.TestCase):
+ MAX = fromHex('0x.fffffffffffff8p+1024') # max normal
+ MIN = fromHex('0x1p-1022') # min normal
+ TINY = fromHex('0x0.0000000000001p-1022') # min subnormal
+ EPS = fromHex('0x0.0000000000001p0') # diff between 1.0 and next float up
+
+ def identical(self, x, y):
+ # check that floats x and y are identical, or that both
+ # are NaNs
+ if isnan(x) or isnan(y):
+ if isnan(x) == isnan(y):
+ return
+ elif x == y and (x != 0.0 or copysign(1.0, x) == copysign(1.0, y)):
+ return
+ self.fail('%r not identical to %r' % (x, y))
+
+ def test_ends(self):
+ self.identical(self.MIN, 2.**-1022)
+ self.identical(self.TINY, 2.**-1074)
+ self.identical(self.EPS, 2.**-52)
+ self.identical(self.MAX, 2.*(2.**1023 - 2.**970))
+
+ def test_invalid_inputs(self):
+ invalid_inputs = [
+ 'infi', # misspelt infinities and nans
+ '-Infinit',
+ '++inf',
+ '-+Inf',
+ '--nan',
+ '+-NaN',
+ 'snan',
+ 'NaNs',
+ 'nna',
+ '0xnan',
+ '',
+ ' ',
+ 'x1.0p0',
+ '0xX1.0p0',
+ '+ 0x1.0p0', # internal whitespace
+ '- 0x1.0p0',
+ '0 x1.0p0',
+ '0x 1.0p0',
+ '0x1 2.0p0',
+ '+0x1 .0p0',
+ '0x1. 0p0',
+ '-0x1.0 1p0',
+ '-0x1.0 p0',
+ '+0x1.0p +0',
+ '0x1.0p -0',
+ '0x1.0p 0',
+ '+0x1.0p+ 0',
+ '-0x1.0p- 0',
+ '++0x1.0p-0', # double signs
+ '--0x1.0p0',
+ '+-0x1.0p+0',
+ '-+0x1.0p0',
+ '0x1.0p++0',
+ '+0x1.0p+-0',
+ '-0x1.0p-+0',
+ '0x1.0p--0',
+ '0x1.0.p0',
+ '0x.p0', # no hex digits before or after point
+ '0x1,p0', # wrong decimal point character
+ '0x1pa',
+ u'0x1p\uff10', # fullwidth Unicode digits
+ u'\uff10x1p0',
+ u'0x\uff11p0',
+ u'0x1.\uff10p0',
+ '0x1p0 \n 0x2p0',
+ '0x1p0\0 0x1p0', # embedded null byte is not end of string
+ ]
+ for x in invalid_inputs:
+ self.assertRaises(ValueError, fromHex, x)
+
+
+ def test_from_hex(self):
+ MIN = self.MIN;
+ MAX = self.MAX;
+ TINY = self.TINY;
+ EPS = self.EPS;
+
+ # two spellings of infinity, with optional signs; case-insensitive
+ self.identical(fromHex('inf'), INF)
+ self.identical(fromHex('+Inf'), INF)
+ self.identical(fromHex('-INF'), -INF)
+ self.identical(fromHex('iNf'), INF)
+ self.identical(fromHex('Infinity'), INF)
+ self.identical(fromHex('+INFINITY'), INF)
+ self.identical(fromHex('-infinity'), -INF)
+ self.identical(fromHex('-iNFiNitY'), -INF)
+
+ # nans with optional sign; case insensitive
+ self.identical(fromHex('nan'), NAN)
+ self.identical(fromHex('+NaN'), NAN)
+ self.identical(fromHex('-NaN'), NAN)
+ self.identical(fromHex('-nAN'), NAN)
+
+ # variations in input format
+ self.identical(fromHex('1'), 1.0)
+ self.identical(fromHex('+1'), 1.0)
+ self.identical(fromHex('1.'), 1.0)
+ self.identical(fromHex('1.0'), 1.0)
+ self.identical(fromHex('1.0p0'), 1.0)
+ self.identical(fromHex('01'), 1.0)
+ self.identical(fromHex('01.'), 1.0)
+ self.identical(fromHex('0x1'), 1.0)
+ self.identical(fromHex('0x1.'), 1.0)
+ self.identical(fromHex('0x1.0'), 1.0)
+ self.identical(fromHex('+0x1.0'), 1.0)
+ self.identical(fromHex('0x1p0'), 1.0)
+ self.identical(fromHex('0X1p0'), 1.0)
+ self.identical(fromHex('0X1P0'), 1.0)
+ self.identical(fromHex('0x1P0'), 1.0)
+ self.identical(fromHex('0x1.p0'), 1.0)
+ self.identical(fromHex('0x1.0p0'), 1.0)
+ self.identical(fromHex('0x.1p4'), 1.0)
+ self.identical(fromHex('0x.1p04'), 1.0)
+ self.identical(fromHex('0x.1p004'), 1.0)
+ self.identical(fromHex('0x1p+0'), 1.0)
+ self.identical(fromHex('0x1P-0'), 1.0)
+ self.identical(fromHex('+0x1p0'), 1.0)
+ self.identical(fromHex('0x01p0'), 1.0)
+ self.identical(fromHex('0x1p00'), 1.0)
+ self.identical(fromHex(u'0x1p0'), 1.0)
+ self.identical(fromHex(' 0x1p0 '), 1.0)
+ self.identical(fromHex('\n 0x1p0'), 1.0)
+ self.identical(fromHex('0x1p0 \t'), 1.0)
+ self.identical(fromHex('0xap0'), 10.0)
+ self.identical(fromHex('0xAp0'), 10.0)
+ self.identical(fromHex('0xaP0'), 10.0)
+ self.identical(fromHex('0xAP0'), 10.0)
+ self.identical(fromHex('0xbep0'), 190.0)
+ self.identical(fromHex('0xBep0'), 190.0)
+ self.identical(fromHex('0xbEp0'), 190.0)
+ self.identical(fromHex('0XBE0P-4'), 190.0)
+ self.identical(fromHex('0xBEp0'), 190.0)
+ self.identical(fromHex('0xB.Ep4'), 190.0)
+ self.identical(fromHex('0x.BEp8'), 190.0)
+ self.identical(fromHex('0x.0BEp12'), 190.0)
+
+ # moving the point around
+ pi = fromHex('0x1.921fb54442d18p1')
+ self.identical(fromHex('0x.006487ed5110b46p11'), pi)
+ self.identical(fromHex('0x.00c90fdaa22168cp10'), pi)
+ self.identical(fromHex('0x.01921fb54442d18p9'), pi)
+ self.identical(fromHex('0x.03243f6a8885a3p8'), pi)
+ self.identical(fromHex('0x.06487ed5110b46p7'), pi)
+ self.identical(fromHex('0x.0c90fdaa22168cp6'), pi)
+ self.identical(fromHex('0x.1921fb54442d18p5'), pi)
+ self.identical(fromHex('0x.3243f6a8885a3p4'), pi)
+ self.identical(fromHex('0x.6487ed5110b46p3'), pi)
+ self.identical(fromHex('0x.c90fdaa22168cp2'), pi)
+ self.identical(fromHex('0x1.921fb54442d18p1'), pi)
+ self.identical(fromHex('0x3.243f6a8885a3p0'), pi)
+ self.identical(fromHex('0x6.487ed5110b46p-1'), pi)
+ self.identical(fromHex('0xc.90fdaa22168cp-2'), pi)
+ self.identical(fromHex('0x19.21fb54442d18p-3'), pi)
+ self.identical(fromHex('0x32.43f6a8885a3p-4'), pi)
+ self.identical(fromHex('0x64.87ed5110b46p-5'), pi)
+ self.identical(fromHex('0xc9.0fdaa22168cp-6'), pi)
+ self.identical(fromHex('0x192.1fb54442d18p-7'), pi)
+ self.identical(fromHex('0x324.3f6a8885a3p-8'), pi)
+ self.identical(fromHex('0x648.7ed5110b46p-9'), pi)
+ self.identical(fromHex('0xc90.fdaa22168cp-10'), pi)
+ self.identical(fromHex('0x1921.fb54442d18p-11'), pi)
+ # ...
+ self.identical(fromHex('0x1921fb54442d1.8p-47'), pi)
+ self.identical(fromHex('0x3243f6a8885a3p-48'), pi)
+ self.identical(fromHex('0x6487ed5110b46p-49'), pi)
+ self.identical(fromHex('0xc90fdaa22168cp-50'), pi)
+ self.identical(fromHex('0x1921fb54442d18p-51'), pi)
+ self.identical(fromHex('0x3243f6a8885a30p-52'), pi)
+ self.identical(fromHex('0x6487ed5110b460p-53'), pi)
+ self.identical(fromHex('0xc90fdaa22168c0p-54'), pi)
+ self.identical(fromHex('0x1921fb54442d180p-55'), pi)
+
+
+ # results that should overflow...
+ self.assertRaises(OverflowError, fromHex, '-0x1p1024')
+ self.assertRaises(OverflowError, fromHex, '0x1p+1025')
+ self.assertRaises(OverflowError, fromHex, '+0X1p1030')
+ self.assertRaises(OverflowError, fromHex, '-0x1p+1100')
+ self.assertRaises(OverflowError, fromHex, '0X1p123456789123456789')
+ self.assertRaises(OverflowError, fromHex, '+0X.8p+1025')
+ self.assertRaises(OverflowError, fromHex, '+0x0.8p1025')
+ self.assertRaises(OverflowError, fromHex, '-0x0.4p1026')
+ self.assertRaises(OverflowError, fromHex, '0X2p+1023')
+ self.assertRaises(OverflowError, fromHex, '0x2.p1023')
+ self.assertRaises(OverflowError, fromHex, '-0x2.0p+1023')
+ self.assertRaises(OverflowError, fromHex, '+0X4p+1022')
+ self.assertRaises(OverflowError, fromHex, '0x1.ffffffffffffffp+1023')
+ self.assertRaises(OverflowError, fromHex, '-0X1.fffffffffffff9p1023')
+ self.assertRaises(OverflowError, fromHex, '0X1.fffffffffffff8p1023')
+ self.assertRaises(OverflowError, fromHex, '+0x3.fffffffffffffp1022')
+ self.assertRaises(OverflowError, fromHex, '0x3fffffffffffffp+970')
+ self.assertRaises(OverflowError, fromHex, '0x10000000000000000p960')
+ self.assertRaises(OverflowError, fromHex, '-0Xffffffffffffffffp960')
+
+ # ...and those that round to +-max float
+ self.identical(fromHex('+0x1.fffffffffffffp+1023'), MAX)
+ self.identical(fromHex('-0X1.fffffffffffff7p1023'), -MAX)
+ self.identical(fromHex('0X1.fffffffffffff7fffffffffffffp1023'), MAX)
+
+ # zeros
+ self.identical(fromHex('0x0p0'), 0.0)
+ self.identical(fromHex('0x0p1000'), 0.0)
+ self.identical(fromHex('-0x0p1023'), -0.0)
+ self.identical(fromHex('0X0p1024'), 0.0)
+ self.identical(fromHex('-0x0p1025'), -0.0)
+ self.identical(fromHex('0X0p2000'), 0.0)
+ self.identical(fromHex('0x0p123456789123456789'), 0.0)
+ self.identical(fromHex('-0X0p-0'), -0.0)
+ self.identical(fromHex('-0X0p-1000'), -0.0)
+ self.identical(fromHex('0x0p-1023'), 0.0)
+ self.identical(fromHex('-0X0p-1024'), -0.0)
+ self.identical(fromHex('-0x0p-1025'), -0.0)
+ self.identical(fromHex('-0x0p-1072'), -0.0)
+ self.identical(fromHex('0X0p-1073'), 0.0)
+ self.identical(fromHex('-0x0p-1074'), -0.0)
+ self.identical(fromHex('0x0p-1075'), 0.0)
+ self.identical(fromHex('0X0p-1076'), 0.0)
+ self.identical(fromHex('-0X0p-2000'), -0.0)
+ self.identical(fromHex('-0x0p-123456789123456789'), -0.0)
+
+ # values that should underflow to 0
+ self.identical(fromHex('0X1p-1075'), 0.0)
+ self.identical(fromHex('-0X1p-1075'), -0.0)
+ self.identical(fromHex('-0x1p-123456789123456789'), -0.0)
+ self.identical(fromHex('0x1.00000000000000001p-1075'), TINY)
+ self.identical(fromHex('-0x1.1p-1075'), -TINY)
+ self.identical(fromHex('0x1.fffffffffffffffffp-1075'), TINY)
+
+ # check round-half-even is working correctly near 0 ...
+ self.identical(fromHex('0x1p-1076'), 0.0)
+ self.identical(fromHex('0X2p-1076'), 0.0)
+ self.identical(fromHex('0X3p-1076'), TINY)
+ self.identical(fromHex('0x4p-1076'), TINY)
+ self.identical(fromHex('0X5p-1076'), TINY)
+ self.identical(fromHex('0X6p-1076'), 2*TINY)
+ self.identical(fromHex('0x7p-1076'), 2*TINY)
+ self.identical(fromHex('0X8p-1076'), 2*TINY)
+ self.identical(fromHex('0X9p-1076'), 2*TINY)
+ self.identical(fromHex('0xap-1076'), 2*TINY)
+ self.identical(fromHex('0Xbp-1076'), 3*TINY)
+ self.identical(fromHex('0xcp-1076'), 3*TINY)
+ self.identical(fromHex('0Xdp-1076'), 3*TINY)
+ self.identical(fromHex('0Xep-1076'), 4*TINY)
+ self.identical(fromHex('0xfp-1076'), 4*TINY)
+ self.identical(fromHex('0x10p-1076'), 4*TINY)
+ self.identical(fromHex('-0x1p-1076'), -0.0)
+ self.identical(fromHex('-0X2p-1076'), -0.0)
+ self.identical(fromHex('-0x3p-1076'), -TINY)
+ self.identical(fromHex('-0X4p-1076'), -TINY)
+ self.identical(fromHex('-0x5p-1076'), -TINY)
+ self.identical(fromHex('-0x6p-1076'), -2*TINY)
+ self.identical(fromHex('-0X7p-1076'), -2*TINY)
+ self.identical(fromHex('-0X8p-1076'), -2*TINY)
+ self.identical(fromHex('-0X9p-1076'), -2*TINY)
+ self.identical(fromHex('-0Xap-1076'), -2*TINY)
+ self.identical(fromHex('-0xbp-1076'), -3*TINY)
+ self.identical(fromHex('-0xcp-1076'), -3*TINY)
+ self.identical(fromHex('-0Xdp-1076'), -3*TINY)
+ self.identical(fromHex('-0xep-1076'), -4*TINY)
+ self.identical(fromHex('-0Xfp-1076'), -4*TINY)
+ self.identical(fromHex('-0X10p-1076'), -4*TINY)
+
+ # ... and near MIN ...
+ self.identical(fromHex('0x0.ffffffffffffd6p-1022'), MIN-3*TINY)
+ self.identical(fromHex('0x0.ffffffffffffd8p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffdap-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffdcp-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffdep-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffe0p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffe2p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffe4p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffe6p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffe8p-1022'), MIN-2*TINY)
+ self.identical(fromHex('0x0.ffffffffffffeap-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.ffffffffffffecp-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.ffffffffffffeep-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.fffffffffffff0p-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.fffffffffffff2p-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.fffffffffffff4p-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.fffffffffffff6p-1022'), MIN-TINY)
+ self.identical(fromHex('0x0.fffffffffffff8p-1022'), MIN)
+ self.identical(fromHex('0x0.fffffffffffffap-1022'), MIN)
+ self.identical(fromHex('0x0.fffffffffffffcp-1022'), MIN)
+ self.identical(fromHex('0x0.fffffffffffffep-1022'), MIN)
+ self.identical(fromHex('0x1.00000000000000p-1022'), MIN)
+ self.identical(fromHex('0x1.00000000000002p-1022'), MIN)
+ self.identical(fromHex('0x1.00000000000004p-1022'), MIN)
+ self.identical(fromHex('0x1.00000000000006p-1022'), MIN)
+ self.identical(fromHex('0x1.00000000000008p-1022'), MIN)
+ self.identical(fromHex('0x1.0000000000000ap-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.0000000000000cp-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.0000000000000ep-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.00000000000010p-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.00000000000012p-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.00000000000014p-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.00000000000016p-1022'), MIN+TINY)
+ self.identical(fromHex('0x1.00000000000018p-1022'), MIN+2*TINY)
+
+ # ... and near 1.0.
+ self.identical(fromHex('0x0.fffffffffffff0p0'), 1.0-EPS)
+ self.identical(fromHex('0x0.fffffffffffff1p0'), 1.0-EPS)
+ self.identical(fromHex('0X0.fffffffffffff2p0'), 1.0-EPS)
+ self.identical(fromHex('0x0.fffffffffffff3p0'), 1.0-EPS)
+ self.identical(fromHex('0X0.fffffffffffff4p0'), 1.0-EPS)
+ self.identical(fromHex('0X0.fffffffffffff5p0'), 1.0-EPS/2)
+ self.identical(fromHex('0X0.fffffffffffff6p0'), 1.0-EPS/2)
+ self.identical(fromHex('0x0.fffffffffffff7p0'), 1.0-EPS/2)
+ self.identical(fromHex('0x0.fffffffffffff8p0'), 1.0-EPS/2)
+ self.identical(fromHex('0X0.fffffffffffff9p0'), 1.0-EPS/2)
+ self.identical(fromHex('0X0.fffffffffffffap0'), 1.0-EPS/2)
+ self.identical(fromHex('0x0.fffffffffffffbp0'), 1.0-EPS/2)
+ self.identical(fromHex('0X0.fffffffffffffcp0'), 1.0)
+ self.identical(fromHex('0x0.fffffffffffffdp0'), 1.0)
+ self.identical(fromHex('0X0.fffffffffffffep0'), 1.0)
+ self.identical(fromHex('0x0.ffffffffffffffp0'), 1.0)
+ self.identical(fromHex('0X1.00000000000000p0'), 1.0)
+ self.identical(fromHex('0X1.00000000000001p0'), 1.0)
+ self.identical(fromHex('0x1.00000000000002p0'), 1.0)
+ self.identical(fromHex('0X1.00000000000003p0'), 1.0)
+ self.identical(fromHex('0x1.00000000000004p0'), 1.0)
+ self.identical(fromHex('0X1.00000000000005p0'), 1.0)
+ self.identical(fromHex('0X1.00000000000006p0'), 1.0)
+ self.identical(fromHex('0X1.00000000000007p0'), 1.0)
+ self.identical(fromHex('0x1.00000000000007ffffffffffffffffffffp0'),
+ 1.0)
+ self.identical(fromHex('0x1.00000000000008p0'), 1.0)
+ self.identical(fromHex('0x1.00000000000008000000000000000001p0'),
+ 1+EPS)
+ self.identical(fromHex('0X1.00000000000009p0'), 1.0+EPS)
+ self.identical(fromHex('0x1.0000000000000ap0'), 1.0+EPS)
+ self.identical(fromHex('0x1.0000000000000bp0'), 1.0+EPS)
+ self.identical(fromHex('0X1.0000000000000cp0'), 1.0+EPS)
+ self.identical(fromHex('0x1.0000000000000dp0'), 1.0+EPS)
+ self.identical(fromHex('0x1.0000000000000ep0'), 1.0+EPS)
+ self.identical(fromHex('0X1.0000000000000fp0'), 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000010p0'), 1.0+EPS)
+ self.identical(fromHex('0X1.00000000000011p0'), 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000012p0'), 1.0+EPS)
+ self.identical(fromHex('0X1.00000000000013p0'), 1.0+EPS)
+ self.identical(fromHex('0X1.00000000000014p0'), 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000015p0'), 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000016p0'), 1.0+EPS)
+ self.identical(fromHex('0X1.00000000000017p0'), 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000017ffffffffffffffffffffp0'),
+ 1.0+EPS)
+ self.identical(fromHex('0x1.00000000000018p0'), 1.0+2*EPS)
+ self.identical(fromHex('0X1.00000000000018000000000000000001p0'),
+ 1.0+2*EPS)
+ self.identical(fromHex('0x1.00000000000019p0'), 1.0+2*EPS)
+ self.identical(fromHex('0X1.0000000000001ap0'), 1.0+2*EPS)
+ self.identical(fromHex('0X1.0000000000001bp0'), 1.0+2*EPS)
+ self.identical(fromHex('0x1.0000000000001cp0'), 1.0+2*EPS)
+ self.identical(fromHex('0x1.0000000000001dp0'), 1.0+2*EPS)
+ self.identical(fromHex('0x1.0000000000001ep0'), 1.0+2*EPS)
+ self.identical(fromHex('0X1.0000000000001fp0'), 1.0+2*EPS)
+ self.identical(fromHex('0x1.00000000000020p0'), 1.0+2*EPS)
+
+ def test_roundtrip(self):
+ def roundtrip(x):
+ return fromHex(toHex(x))
+
+ for x in [NAN, INF, self.MAX, self.MIN, self.MIN-self.TINY, self.TINY, 0.0]:
+ self.identical(x, roundtrip(x))
+ self.identical(-x, roundtrip(-x))
+
+ # fromHex(toHex(x)) should exactly recover x, for any non-NaN float x.
+ import random
+ for i in xrange(10000):
+ e = random.randrange(-1200, 1200)
+ m = random.random()
+ s = random.choice([1.0, -1.0])
+ try:
+ x = s*ldexp(m, e)
+ except OverflowError:
+ pass
+ else:
+ self.identical(x, fromHex(toHex(x)))
+
def test_main():
test_support.run_unittest(
@@ -351,6 +735,7 @@
IEEEFormatTestCase,
ReprTestCase,
InfNanTest,
+ HexFloatTestCase,
)
if __name__ == '__main__':
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS (original)
+++ python/trunk/Misc/NEWS Tue Jul 15 21:08:33 2008
@@ -10,6 +10,10 @@
Core and Builtins
-----------------
+- Issue #3008: the float type has a new instance method 'float.hex'
+ and a new class method 'float.fromhex' to convert floating-point
+ numbers to and from hexadecimal strings, respectively.
+
- Issue #2235: __hash__ is once again inherited by default. To allow
collections.Hashable to remain meaningful in the presence of the
default hash implementation (object.__hash__), it is now possible
Modified: python/trunk/Objects/floatobject.c
==============================================================================
--- python/trunk/Objects/floatobject.c (original)
+++ python/trunk/Objects/floatobject.c Tue Jul 15 21:08:33 2008
@@ -10,6 +10,11 @@
#include <ctype.h>
#include <float.h>
+#undef MAX
+#undef MIN
+#define MAX(x, y) ((x) < (y) ? (y) : (x))
+#define MIN(x, y) ((x) < (y) ? (x) : (y))
+
#ifdef HAVE_IEEEFP_H
#include <ieeefp.h>
#endif
@@ -1109,6 +1114,404 @@
return v;
}
+/* turn ASCII hex characters into integer values and vice versa */
+
+static char
+char_from_hex(int x)
+{
+ assert(0 <= x && x < 16);
+ return "0123456789abcdef"[x];
+}
+
+static int
+hex_from_char(char c) {
+ int x;
+ assert(isxdigit(c));
+ switch(c) {
+ case '0':
+ x = 0;
+ break;
+ case '1':
+ x = 1;
+ break;
+ case '2':
+ x = 2;
+ break;
+ case '3':
+ x = 3;
+ break;
+ case '4':
+ x = 4;
+ break;
+ case '5':
+ x = 5;
+ break;
+ case '6':
+ x = 6;
+ break;
+ case '7':
+ x = 7;
+ break;
+ case '8':
+ x = 8;
+ break;
+ case '9':
+ x = 9;
+ break;
+ case 'a':
+ case 'A':
+ x = 10;
+ break;
+ case 'b':
+ case 'B':
+ x = 11;
+ break;
+ case 'c':
+ case 'C':
+ x = 12;
+ break;
+ case 'd':
+ case 'D':
+ x = 13;
+ break;
+ case 'e':
+ case 'E':
+ x = 14;
+ break;
+ case 'f':
+ case 'F':
+ x = 15;
+ break;
+ default:
+ x = -1;
+ break;
+ }
+ return x;
+}
+
+/* convert a float to a hexadecimal string */
+
+/* TOHEX_NBITS is DBL_MANT_DIG rounded up to the next integer
+ of the form 4k+1. */
+#define TOHEX_NBITS DBL_MANT_DIG + 3 - (DBL_MANT_DIG+2)%4
+
+static PyObject *
+float_hex(PyObject *v)
+{
+ double x, m;
+ int e, shift, i, si, esign;
+ /* Space for 1+(TOHEX_NBITS-1)/4 digits, a decimal point, and the
+ trailing NUL byte. */
+ char s[(TOHEX_NBITS-1)/4+3];
+
+ CONVERT_TO_DOUBLE(v, x);
+
+ if (Py_IS_NAN(x) || Py_IS_INFINITY(x))
+ return float_str((PyFloatObject *)v);
+
+ if (x == 0.0) {
+ if(copysign(1.0, x) == -1.0)
+ return PyString_FromString("-0x0.0p+0");
+ else
+ return PyString_FromString("0x0.0p+0");
+ }
+
+ m = frexp(fabs(x), &e);
+ shift = 1 - MAX(DBL_MIN_EXP - e, 0);
+ m = ldexp(m, shift);
+ e -= shift;
+
+ si = 0;
+ s[si] = char_from_hex((int)m);
+ si++;
+ m -= (int)m;
+ s[si] = '.';
+ si++;
+ for (i=0; i < (TOHEX_NBITS-1)/4; i++) {
+ m *= 16.0;
+ s[si] = char_from_hex((int)m);
+ si++;
+ m -= (int)m;
+ }
+ s[si] = '\0';
+
+ if (e < 0) {
+ esign = (int)'-';
+ e = -e;
+ }
+ else
+ esign = (int)'+';
+
+ if (x < 0.0)
+ return PyString_FromFormat("-0x%sp%c%d", s, esign, e);
+ else
+ return PyString_FromFormat("0x%sp%c%d", s, esign, e);
+}
+
+PyDoc_STRVAR(float_hex_doc,
+"float.hex() -> string\n\
+\n\
+Return a hexadecimal representation of a floating-point number.\n\
+>>> (-0.1).hex()\n\
+'-0x1.999999999999ap-4'\n\
+>>> 3.14159.hex()\n\
+'0x1.921f9f01b866ep+1'");
+
+/* Convert a hexadecimal string to a float. */
+
+static PyObject *
+float_fromhex(PyObject *cls, PyObject *arg)
+{
+ PyObject *result_as_float, *result;
+ double x;
+ long exp, top_exp, lsb, key_digit;
+ char *s, *coeff_start, *s_store, *coeff_end, *exp_start, *s_end;
+ int half_eps, digit, round_up, sign=1;
+ Py_ssize_t length, ndigits, fdigits, i;
+
+ /*
+ * For the sake of simplicity and correctness, we impose an artificial
+ * limit on ndigits, the total number of hex digits in the coefficient
+ * The limit is chosen to ensure that, writing exp for the exponent,
+ *
+ * (1) if exp > LONG_MAX/2 then the value of the hex string is
+ * guaranteed to overflow (provided it's nonzero)
+ *
+ * (2) if exp < LONG_MIN/2 then the value of the hex string is
+ * guaranteed to underflow to 0.
+ *
+ * (3) if LONG_MIN/2 <= exp <= LONG_MAX/2 then there's no danger of
+ * overflow in the calculation of exp and top_exp below.
+ *
+ * More specifically, ndigits is assumed to satisfy the following
+ * inequalities:
+ *
+ * 4*ndigits <= DBL_MIN_EXP - DBL_MANT_DIG - LONG_MIN/2
+ * 4*ndigits <= LONG_MAX/2 + 1 - DBL_MAX_EXP
+ *
+ * If either of these inequalities is not satisfied, a ValueError is
+ * raised. Otherwise, write x for the value of the hex string, and
+ * assume x is nonzero. Then
+ *
+ * 2**(exp-4*ndigits) <= |x| < 2**(exp+4*ndigits).
+ *
+ * Now if exp > LONG_MAX/2 then:
+ *
+ * exp - 4*ndigits >= LONG_MAX/2 + 1 - (LONG_MAX/2 + 1 - DBL_MAX_EXP)
+ * = DBL_MAX_EXP
+ *
+ * so |x| >= 2**DBL_MAX_EXP, which is too large to be stored in C
+ * double, so overflows. If exp < LONG_MIN/2, then
+ *
+ * exp + 4*ndigits <= LONG_MIN/2 - 1 + (
+ * DBL_MIN_EXP - DBL_MANT_DIG - LONG_MIN/2)
+ * = DBL_MIN_EXP - DBL_MANT_DIG - 1
+ *
+ * and so |x| < 2**(DBL_MIN_EXP-DBL_MANT_DIG-1), hence underflows to 0
+ * when converted to a C double.
+ *
+ * It's easy to show that if LONG_MIN/2 <= exp <= LONG_MAX/2 then both
+ * exp+4*ndigits and exp-4*ndigits are within the range of a long.
+ */
+
+ if (PyString_AsStringAndSize(arg, &s, &length))
+ return NULL;
+ s_end = s + length;
+
+ /********************
+ * Parse the string *
+ ********************/
+
+ /* leading whitespace and optional sign */
+ while (isspace(*s))
+ s++;
+ if (*s == '-') {
+ s++;
+ sign = -1;
+ }
+ else if (*s == '+')
+ s++;
+
+ /* infinities and nans */
+ if (PyOS_mystrnicmp(s, "nan", 4) == 0) {
+ x = Py_NAN;
+ goto finished;
+ }
+ if (PyOS_mystrnicmp(s, "inf", 4) == 0 ||
+ PyOS_mystrnicmp(s, "infinity", 9) == 0) {
+ x = sign*Py_HUGE_VAL;
+ goto finished;
+ }
+
+ /* [0x] */
+ s_store = s;
+ if (*s == '0') {
+ s++;
+ if (tolower(*s) == (int)'x')
+ s++;
+ else
+ s = s_store;
+ }
+
+ /* coefficient: <integer> [. <fraction>] */
+ coeff_start = s;
+ while (isxdigit(*s))
+ s++;
+ s_store = s;
+ if (*s == '.') {
+ s++;
+ while (isxdigit(*s))
+ s++;
+ coeff_end = s-1;
+ }
+ else
+ coeff_end = s;
+
+ /* ndigits = total # of hex digits; fdigits = # after point */
+ ndigits = coeff_end - coeff_start;
+ fdigits = coeff_end - s_store;
+ if (ndigits == 0)
+ goto parse_error;
+ if (ndigits > MIN(DBL_MIN_EXP - DBL_MANT_DIG - LONG_MIN/2,
+ LONG_MAX/2 + 1 - DBL_MAX_EXP)/4)
+ goto insane_length_error;
+
+ /* [p <exponent>] */
+ if (tolower(*s) == (int)'p') {
+ s++;
+ exp_start = s;
+ if (*s == '-' || *s == '+')
+ s++;
+ if (!isdigit(*s))
+ goto parse_error;
+ s++;
+ while (isdigit(*s))
+ s++;
+ exp = strtol(exp_start, NULL, 10);
+ }
+ else
+ exp = 0;
+
+ /* optional trailing whitespace leading to the end of the string */
+ while (isspace(*s))
+ s++;
+ if (s != s_end)
+ goto parse_error;
+
+/* for 0 <= j < ndigits, HEX_DIGIT(j) gives the jth most significant digit */
+#define HEX_DIGIT(j) hex_from_char(*((j) < fdigits ? \
+ coeff_end-(j) : \
+ coeff_end-1-(j)))
+
+ /*******************************************
+ * Compute rounded value of the hex string *
+ *******************************************/
+
+ /* Discard leading zeros, and catch extreme overflow and underflow */
+ while (ndigits > 0 && HEX_DIGIT(ndigits-1) == 0)
+ ndigits--;
+ if (ndigits == 0 || exp < LONG_MIN/2) {
+ x = sign * 0.0;
+ goto finished;
+ }
+ if (exp > LONG_MAX/2)
+ goto overflow_error;
+
+ /* Adjust exponent for fractional part. */
+ exp = exp - 4*((long)fdigits);
+
+ /* top_exp = 1 more than exponent of most sig. bit of coefficient */
+ top_exp = exp + 4*((long)ndigits - 1);
+ for (digit = HEX_DIGIT(ndigits-1); digit != 0; digit /= 2)
+ top_exp++;
+
+ /* catch almost all nonextreme cases of overflow and underflow here */
+ if (top_exp < DBL_MIN_EXP - DBL_MANT_DIG) {
+ x = sign * 0.0;
+ goto finished;
+ }
+ if (top_exp > DBL_MAX_EXP)
+ goto overflow_error;
+
+ /* lsb = exponent of least significant bit of the *rounded* value.
+ This is top_exp - DBL_MANT_DIG unless result is subnormal. */
+ lsb = MAX(top_exp, (long)DBL_MIN_EXP) - DBL_MANT_DIG;
+
+ x = 0.0;
+ if (exp >= lsb) {
+ /* no rounding required */
+ for (i = ndigits-1; i >= 0; i--)
+ x = 16.0*x + HEX_DIGIT(i);
+ x = sign * ldexp(x, (int)(exp));
+ goto finished;
+ }
+ /* rounding required. key_digit is the index of the hex digit
+ containing the first bit to be rounded away. */
+ half_eps = 1 << (int)((lsb - exp - 1) % 4);
+ key_digit = (lsb - exp - 1) / 4;
+ for (i = ndigits-1; i > key_digit; i--)
+ x = 16.0*x + HEX_DIGIT(i);
+ digit = HEX_DIGIT(key_digit);
+ x = 16.0*x + (double)(digit & (16-2*half_eps));
+
+ /* round-half-even: round up if bit lsb-1 is 1 and at least one of
+ bits lsb, lsb-2, lsb-3, lsb-4, ... is 1. */
+ if ((digit & half_eps) != 0) {
+ round_up = 0;
+ if ((digit & (3*half_eps-1)) != 0 ||
+ (half_eps == 8 && (HEX_DIGIT(key_digit+1) & 1) != 0))
+ round_up = 1;
+ else
+ for (i = key_digit-1; i >= 0; i--)
+ if (HEX_DIGIT(i) != 0) {
+ round_up = 1;
+ break;
+ }
+ if (round_up == 1) {
+ x += 2*half_eps;
+ if (top_exp == DBL_MAX_EXP &&
+ x == ldexp((double)(2*half_eps), DBL_MANT_DIG))
+ /* overflow corner case: pre-rounded value <
+ 2**DBL_MAX_EXP; rounded=2**DBL_MAX_EXP. */
+ goto overflow_error;
+ }
+ }
+ x = sign * ldexp(x, (int)(exp+4*key_digit));
+
+ finished:
+ result_as_float = Py_BuildValue("(d)", x);
+ if (result_as_float == NULL)
+ return NULL;
+ result = PyObject_CallObject(cls, result_as_float);
+ Py_DECREF(result_as_float);
+ return result;
+
+ overflow_error:
+ PyErr_SetString(PyExc_OverflowError,
+ "hexadecimal value too large to represent as a float");
+ return NULL;
+
+ parse_error:
+ PyErr_SetString(PyExc_ValueError,
+ "invalid hexadecimal floating-point string");
+ return NULL;
+
+ insane_length_error:
+ PyErr_SetString(PyExc_ValueError,
+ "hexadecimal string too long to convert");
+ return NULL;
+}
+
+PyDoc_STRVAR(float_fromhex_doc,
+"float.fromhex(string) -> float\n\
+\n\
+Create a floating-point number from a hexadecimal string.\n\
+>>> float.fromhex('0x1.ffffp10')\n\
+2047.984375\n\
+>>> float.fromhex('-0x1p-1074')\n\
+-4.9406564584124654e-324");
+
+
static PyObject *
float_as_integer_ratio(PyObject *v, PyObject *unused)
{
@@ -1433,6 +1836,10 @@
"Returns the Integral closest to x between 0 and x."},
{"as_integer_ratio", (PyCFunction)float_as_integer_ratio, METH_NOARGS,
float_as_integer_ratio_doc},
+ {"fromhex", (PyCFunction)float_fromhex,
+ METH_O|METH_CLASS, float_fromhex_doc},
+ {"hex", (PyCFunction)float_hex,
+ METH_NOARGS, float_hex_doc},
{"is_integer", (PyCFunction)float_is_integer, METH_NOARGS,
"Returns True if the float is an integer."},
#if 0
More information about the Python-checkins
mailing list