From f8476c15730939c4ee64d94f08c2d6e40b09195d Mon Sep 17 00:00:00 2001 From: Mark Dickinson Date: Fri, 9 May 2008 17:54:23 +0000 Subject: Issue #2487. math.ldexp(x, n) raised OverflowError when n was large and negative; fix to return an (appropriately signed) zero instead. --- Lib/test/test_math.py | 18 ++++++++++++++ Misc/NEWS | 5 ++++ Modules/mathmodule.c | 66 +++++++++++++++++++++++++++++++++++++++++---------- 3 files changed, 77 insertions(+), 12 deletions(-) diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py index c9eade3..a5c6f62 100644 --- a/Lib/test/test_math.py +++ b/Lib/test/test_math.py @@ -374,6 +374,24 @@ class MathTests(unittest.TestCase): self.assertEquals(math.ldexp(NINF, -213), NINF) self.assert_(math.isnan(math.ldexp(NAN, 0))) + # large second argument + for n in [10**5, 10L**5, 10**10, 10L**10, 10**20, 10**40]: + self.assertEquals(math.ldexp(INF, -n), INF) + self.assertEquals(math.ldexp(NINF, -n), NINF) + self.assertEquals(math.ldexp(1., -n), 0.) + self.assertEquals(math.ldexp(-1., -n), -0.) + self.assertEquals(math.ldexp(0., -n), 0.) + self.assertEquals(math.ldexp(-0., -n), -0.) + self.assert_(math.isnan(math.ldexp(NAN, -n))) + + self.assertRaises(OverflowError, math.ldexp, 1., n) + self.assertRaises(OverflowError, math.ldexp, -1., n) + self.assertEquals(math.ldexp(0., n), 0.) + self.assertEquals(math.ldexp(-0., n), -0.) + self.assertEquals(math.ldexp(INF, n), INF) + self.assertEquals(math.ldexp(NINF, n), NINF) + self.assert_(math.isnan(math.ldexp(NAN, n))) + def testLog(self): self.assertRaises(TypeError, math.log) self.ftest('log(1/e)', math.log(1/math.e), -1) diff --git a/Misc/NEWS b/Misc/NEWS index 12522db..2b7b52f 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -23,6 +23,11 @@ Extension Modules Library ------- +- Issue #2487: change the semantics of math.ldexp(x, n) when n is too + large to fit in a C long. ldexp(x, n) now returns a zero (with + suitable sign) if n is large and negative; previously, it raised + OverflowError. + - The toaiff module has been deprecated for removal in Python 3.0. - The test.testall module has been deprecated for removal in Python 3.0. diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c index 201ffc4..c4ac69a 100644 --- a/Modules/mathmodule.c +++ b/Modules/mathmodule.c @@ -349,23 +349,65 @@ static PyObject * math_ldexp(PyObject *self, PyObject *args) { double x, r; - int exp; - if (! PyArg_ParseTuple(args, "di:ldexp", &x, &exp)) + PyObject *oexp; + long exp; + if (! PyArg_ParseTuple(args, "dO:ldexp", &x, &oexp)) return NULL; - errno = 0; - PyFPE_START_PROTECT("in math_ldexp", return 0) - r = ldexp(x, exp); - PyFPE_END_PROTECT(r) - if (Py_IS_FINITE(x) && Py_IS_INFINITY(r)) + + if (PyLong_Check(oexp)) { + /* on overflow, replace exponent with either LONG_MAX + or LONG_MIN, depending on the sign. */ + exp = PyLong_AsLong(oexp); + if (exp == -1 && PyErr_Occurred()) { + if (PyErr_ExceptionMatches(PyExc_OverflowError)) { + if (Py_SIZE(oexp) < 0) { + exp = LONG_MIN; + } + else { + exp = LONG_MAX; + } + PyErr_Clear(); + } + else { + /* propagate any unexpected exception */ + return NULL; + } + } + } + else if (PyInt_Check(oexp)) { + exp = PyInt_AS_LONG(oexp); + } + else { + PyErr_SetString(PyExc_TypeError, + "Expected an int or long as second argument " + "to ldexp."); + return NULL; + } + + if (x == 0. || !Py_IS_FINITE(x)) { + /* NaNs, zeros and infinities are returned unchanged */ + r = x; + errno = 0; + } else if (exp > INT_MAX) { + /* overflow */ + r = copysign(Py_HUGE_VAL, x); errno = ERANGE; - /* Windows MSVC8 sets errno = EDOM on ldexp(NaN, i); - we unset it to avoid raising a ValueError here. */ - if (errno == EDOM) + } else if (exp < INT_MIN) { + /* underflow to +-0 */ + r = copysign(0., x); errno = 0; + } else { + errno = 0; + PyFPE_START_PROTECT("in math_ldexp", return 0); + r = ldexp(x, (int)exp); + PyFPE_END_PROTECT(r); + if (Py_IS_INFINITY(r)) + errno = ERANGE; + } + if (errno && is_error(r)) return NULL; - else - return PyFloat_FromDouble(r); + return PyFloat_FromDouble(r); } PyDoc_STRVAR(math_ldexp_doc, -- cgit v0.12