Author: Amaury Forgeot d'Arc <amaur...@gmail.com>
Branch: merge-2.7.2
Changeset: r51654:40000ebe74d7
Date: 2012-01-22 18:31 +0100
http://bitbucket.org/pypy/pypy/changeset/40000ebe74d7/
Log: Fix edge cases in float.__mod__
diff --git a/pypy/objspace/std/floatobject.py b/pypy/objspace/std/floatobject.py
--- a/pypy/objspace/std/floatobject.py
+++ b/pypy/objspace/std/floatobject.py
@@ -383,8 +383,16 @@
except ValueError:
mod = rfloat.NAN
else:
- if (mod and ((y < 0.0) != (mod < 0.0))):
- mod += y
+ if mod:
+ # ensure the remainder has the same sign as the denominator
+ if (y < 0.0) != (mod < 0.0):
+ mod += y
+ else:
+ # the remainder is zero, and in the presence of signed zeroes
+ # fmod returns different results across platforms; ensure
+ # it has the same sign as the denominator; we'd like to do
+ # "mod = y * 0.0", but that may get optimized away
+ mod = copysign(0.0, y)
return W_FloatObject(mod)
diff --git a/pypy/objspace/std/test/test_floatobject.py
b/pypy/objspace/std/test/test_floatobject.py
--- a/pypy/objspace/std/test/test_floatobject.py
+++ b/pypy/objspace/std/test/test_floatobject.py
@@ -789,3 +789,26 @@
raises(ZeroDivisionError, lambda: inf % 0)
raises(ZeroDivisionError, lambda: inf // 0)
raises(ZeroDivisionError, divmod, inf, 0)
+
+ def test_modulo_edgecases(self):
+ # Check behaviour of % operator for IEEE 754 special cases.
+ # In particular, check signs of zeros.
+ mod = float.__mod__
+ import math
+
+ def check(a, b):
+ assert (a, math.copysign(1.0, a)) == (b, math.copysign(1.0, b))
+
+ check(mod(-1.0, 1.0), 0.0)
+ check(mod(-1e-100, 1.0), 1.0)
+ check(mod(-0.0, 1.0), 0.0)
+ check(mod(0.0, 1.0), 0.0)
+ check(mod(1e-100, 1.0), 1e-100)
+ check(mod(1.0, 1.0), 0.0)
+
+ check(mod(-1.0, -1.0), -0.0)
+ check(mod(-1e-100, -1.0), -1e-100)
+ check(mod(-0.0, -1.0), -0.0)
+ check(mod(0.0, -1.0), -0.0)
+ check(mod(1e-100, -1.0), -1.0)
+ check(mod(1.0, -1.0), -0.0)
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