Moved Rational._binary_float_to_ratio() to float.as_integer_ratio() because
it's useful outside of rational numbers.
This is my first C code that had to do anything significant. Please be more
careful when looking over it.
diff --git a/Lib/rational.py b/Lib/rational.py
index 8ee38ba..99c5ff6 100755
--- a/Lib/rational.py
+++ b/Lib/rational.py
@@ -25,60 +25,6 @@
return a
-def _binary_float_to_ratio(x):
- """x -> (top, bot), a pair of ints s.t. x = top/bot.
-
- The conversion is done exactly, without rounding.
- bot > 0 guaranteed.
- Some form of binary fp is assumed.
- Pass NaNs or infinities at your own risk.
-
- >>> _binary_float_to_ratio(10.0)
- (10, 1)
- >>> _binary_float_to_ratio(0.0)
- (0, 1)
- >>> _binary_float_to_ratio(-.25)
- (-1, 4)
- """
- # XXX Move this to floatobject.c with a name like
- # float.as_integer_ratio()
-
- if x == 0:
- return 0, 1
- f, e = math.frexp(x)
- signbit = 1
- if f < 0:
- f = -f
- signbit = -1
- assert 0.5 <= f < 1.0
- # x = signbit * f * 2**e exactly
-
- # Suck up CHUNK bits at a time; 28 is enough so that we suck
- # up all bits in 2 iterations for all known binary double-
- # precision formats, and small enough to fit in an int.
- CHUNK = 28
- top = 0
- # invariant: x = signbit * (top + f) * 2**e exactly
- while f:
- f = math.ldexp(f, CHUNK)
- digit = trunc(f)
- assert digit >> CHUNK == 0
- top = (top << CHUNK) | digit
- f = f - digit
- assert 0.0 <= f < 1.0
- e = e - CHUNK
- assert top
-
- # Add in the sign bit.
- top = signbit * top
-
- # now x = top * 2**e exactly; fold in 2**e
- if e>0:
- return (top * 2**e, 1)
- else:
- return (top, 2 ** -e)
-
-
_RATIONAL_FORMAT = re.compile(
r'^\s*(?P<sign>[-+]?)(?P<num>\d+)'
r'(?:/(?P<denom>\d+)|\.(?P<decimal>\d+))?\s*$')
@@ -163,7 +109,7 @@
(cls.__name__, f, type(f).__name__))
if math.isnan(f) or math.isinf(f):
raise TypeError("Cannot convert %r to %s." % (f, cls.__name__))
- return cls(*_binary_float_to_ratio(f))
+ return cls(*f.as_integer_ratio())
@classmethod
def from_decimal(cls, dec):
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index f7b7c0c..a1e2a12 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -5,7 +5,7 @@
run_unittest, run_with_locale
from operator import neg
-import sys, warnings, cStringIO, random, UserDict
+import sys, warnings, cStringIO, random, rational, UserDict
warnings.filterwarnings("ignore", "hex../oct.. of negative int",
FutureWarning, __name__)
warnings.filterwarnings("ignore", "integer argument expected",
@@ -688,6 +688,25 @@
self.assertAlmostEqual(float(Foo3(21)), 42.)
self.assertRaises(TypeError, float, Foo4(42))
+ def test_floatasratio(self):
+ R = rational.Rational
+ self.assertEqual(R(0, 1),
+ R(*float(0.0).as_integer_ratio()))
+ self.assertEqual(R(5, 2),
+ R(*float(2.5).as_integer_ratio()))
+ self.assertEqual(R(1, 2),
+ R(*float(0.5).as_integer_ratio()))
+ self.assertEqual(R(4728779608739021, 2251799813685248),
+ R(*float(2.1).as_integer_ratio()))
+ self.assertEqual(R(-4728779608739021, 2251799813685248),
+ R(*float(-2.1).as_integer_ratio()))
+ self.assertEqual(R(-2100, 1),
+ R(*float(-2100.0).as_integer_ratio()))
+
+ self.assertRaises(OverflowError, float('inf').as_integer_ratio)
+ self.assertRaises(OverflowError, float('-inf').as_integer_ratio)
+ self.assertRaises(ValueError, float('nan').as_integer_ratio)
+
def test_getattr(self):
import sys
self.assert_(getattr(sys, 'stdout') is sys.stdout)