Issue python#29282: Backed out changeset b33012ef1417

mdickinson · mdickinson · commit 5e65cd39dfe7 · 2017-01-21T13:10:52.000Z
diff --git a/Doc/library/math.rst b/Doc/library/math.rst
@@ -57,21 +57,6 @@ Number-theoretic and representation functions
    If *x* is not a float, delegates to ``x.__floor__()``, which should return an
    :class:`~numbers.Integral` value.
 
-.. function:: fma(x, y, z)
-
-   Fused multiply-add operation. Return ``(x * y) + z``, computed as though with
-   infinite precision and range followed by a single round to the ``float``
-   format. This operation often provides better accuracy than the direct
-   expression ``(x * y) + z``.
-
-   This function follows the specification of the fusedMultiplyAdd operation
-   described in the IEEE 754-2008 standard. The standard leaves one case
-   implementation-defined, namely the result of ``fma(0, inf, nan)``
-   and ``fma(inf, 0, nan)``. In these cases, ``math.fma`` returns a NaN,
-   and does not raise any exception.
-
-   .. versionadded:: 3.7
-
 
 .. function:: fmod(x, y)
 
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
@@ -100,15 +100,6 @@ The :const:`~unittest.mock.sentinel` attributes now preserve their identity
 when they are :mod:`copied <copy>` or :mod:`pickled <pickle>`.
 (Contributed by Serhiy Storchaka in :issue:`20804`.)
 
-math module
------------
-
-A new function :func:`~math.fma` for fused multiply-add operations has been
-added. This function computes ``x * y + z`` with only a single round, and so
-avoids any intermediate loss of precision. It wraps the ``fma`` function
-provided by C99, and follows the specification of the IEEE 754-2008
-"fusedMultiplyAdd" operation for special cases.
-
 
 Optimizations
 =============
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
@@ -4,7 +4,6 @@
 from test.support import run_unittest, verbose, requires_IEEE_754
 from test import support
 import unittest
-import itertools
 import math
 import os
 import platform
@@ -1411,244 +1410,11 @@ def test_fractions(self):
         self.assertAllNotClose(fraction_examples, rel_tol=1e-9)
 
 
-class FMATests(unittest.TestCase):
-    """ Tests for math.fma. """
-
-    def test_fma_nan_results(self):
-        # Selected representative values.
-        values = [
-            -math.inf, -1e300, -2.3, -1e-300, -0.0,
-            0.0, 1e-300, 2.3, 1e300, math.inf, math.nan
-        ]
-
-        # If any input is a NaN, the result should be a NaN, too.
-        for a, b in itertools.product(values, repeat=2):
-            self.assertIsNaN(math.fma(math.nan, a, b))
-            self.assertIsNaN(math.fma(a, math.nan, b))
-            self.assertIsNaN(math.fma(a, b, math.nan))
-
-    def test_fma_infinities(self):
-        # Cases involving infinite inputs or results.
-        positives = [1e-300, 2.3, 1e300, math.inf]
-        finites = [-1e300, -2.3, -1e-300, -0.0, 0.0, 1e-300, 2.3, 1e300]
-        non_nans = [-math.inf, -2.3, -0.0, 0.0, 2.3, math.inf]
-
-        # ValueError due to inf * 0 computation.
-        for c in non_nans:
-            for infinity in [math.inf, -math.inf]:
-                for zero in [0.0, -0.0]:
-                    with self.assertRaises(ValueError):
-                        math.fma(infinity, zero, c)
-                    with self.assertRaises(ValueError):
-                        math.fma(zero, infinity, c)
-
-        # ValueError when a*b and c both infinite of opposite signs.
-        for b in positives:
-            with self.assertRaises(ValueError):
-                math.fma(math.inf, b, -math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(math.inf, -b, math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(-math.inf, -b, -math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(-math.inf, b, math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(b, math.inf, -math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(-b, math.inf, math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(-b, -math.inf, -math.inf)
-            with self.assertRaises(ValueError):
-                math.fma(b, -math.inf, math.inf)
-
-        # Infinite result when a*b and c both infinite of the same sign.
-        for b in positives:
-            self.assertEqual(math.fma(math.inf, b, math.inf), math.inf)
-            self.assertEqual(math.fma(math.inf, -b, -math.inf), -math.inf)
-            self.assertEqual(math.fma(-math.inf, -b, math.inf), math.inf)
-            self.assertEqual(math.fma(-math.inf, b, -math.inf), -math.inf)
-            self.assertEqual(math.fma(b, math.inf, math.inf), math.inf)
-            self.assertEqual(math.fma(-b, math.inf, -math.inf), -math.inf)
-            self.assertEqual(math.fma(-b, -math.inf, math.inf), math.inf)
-            self.assertEqual(math.fma(b, -math.inf, -math.inf), -math.inf)
-
-        # Infinite result when a*b finite, c infinite.
-        for a, b in itertools.product(finites, finites):
-            self.assertEqual(math.fma(a, b, math.inf), math.inf)
-            self.assertEqual(math.fma(a, b, -math.inf), -math.inf)
-
-        # Infinite result when a*b infinite, c finite.
-        for b, c in itertools.product(positives, finites):
-            self.assertEqual(math.fma(math.inf, b, c), math.inf)
-            self.assertEqual(math.fma(-math.inf, b, c), -math.inf)
-            self.assertEqual(math.fma(-math.inf, -b, c), math.inf)
-            self.assertEqual(math.fma(math.inf, -b, c), -math.inf)
-
-            self.assertEqual(math.fma(b, math.inf, c), math.inf)
-            self.assertEqual(math.fma(b, -math.inf, c), -math.inf)
-            self.assertEqual(math.fma(-b, -math.inf, c), math.inf)
-            self.assertEqual(math.fma(-b, math.inf, c), -math.inf)
-
-    def test_fma_zero_result(self):
-        nonnegative_finites = [0.0, 1e-300, 2.3, 1e300]
-
-        # Zero results from exact zero inputs.
-        for b in nonnegative_finites:
-            self.assertIsPositiveZero(math.fma(0.0, b, 0.0))
-            self.assertIsPositiveZero(math.fma(0.0, b, -0.0))
-            self.assertIsNegativeZero(math.fma(0.0, -b, -0.0))
-            self.assertIsPositiveZero(math.fma(0.0, -b, 0.0))
-            self.assertIsPositiveZero(math.fma(-0.0, -b, 0.0))
-            self.assertIsPositiveZero(math.fma(-0.0, -b, -0.0))
-            self.assertIsNegativeZero(math.fma(-0.0, b, -0.0))
-            self.assertIsPositiveZero(math.fma(-0.0, b, 0.0))
-
-            self.assertIsPositiveZero(math.fma(b, 0.0, 0.0))
-            self.assertIsPositiveZero(math.fma(b, 0.0, -0.0))
-            self.assertIsNegativeZero(math.fma(-b, 0.0, -0.0))
-            self.assertIsPositiveZero(math.fma(-b, 0.0, 0.0))
-            self.assertIsPositiveZero(math.fma(-b, -0.0, 0.0))
-            self.assertIsPositiveZero(math.fma(-b, -0.0, -0.0))
-            self.assertIsNegativeZero(math.fma(b, -0.0, -0.0))
-            self.assertIsPositiveZero(math.fma(b, -0.0, 0.0))
-
-        # Exact zero result from nonzero inputs.
-        self.assertIsPositiveZero(math.fma(2.0, 2.0, -4.0))
-        self.assertIsPositiveZero(math.fma(2.0, -2.0, 4.0))
-        self.assertIsPositiveZero(math.fma(-2.0, -2.0, -4.0))
-        self.assertIsPositiveZero(math.fma(-2.0, 2.0, 4.0))
-
-        # Underflow to zero.
-        tiny = 1e-300
-        self.assertIsPositiveZero(math.fma(tiny, tiny, 0.0))
-        self.assertIsNegativeZero(math.fma(tiny, -tiny, 0.0))
-        self.assertIsPositiveZero(math.fma(-tiny, -tiny, 0.0))
-        self.assertIsNegativeZero(math.fma(-tiny, tiny, 0.0))
-        self.assertIsPositiveZero(math.fma(tiny, tiny, -0.0))
-        self.assertIsNegativeZero(math.fma(tiny, -tiny, -0.0))
-        self.assertIsPositiveZero(math.fma(-tiny, -tiny, -0.0))
-        self.assertIsNegativeZero(math.fma(-tiny, tiny, -0.0))
-
-        # Corner case where rounding the multiplication would
-        # give the wrong result.
-        x = float.fromhex('0x1p-500')
-        y = float.fromhex('0x1p-550')
-        z = float.fromhex('0x1p-1000')
-        self.assertIsNegativeZero(math.fma(x-y, x+y, -z))
-        self.assertIsPositiveZero(math.fma(y-x, x+y, z))
-        self.assertIsNegativeZero(math.fma(y-x, -(x+y), -z))
-        self.assertIsPositiveZero(math.fma(x-y, -(x+y), z))
-
-    def test_fma_overflow(self):
-        a = b = float.fromhex('0x1p512')
-        c = float.fromhex('0x1p1023')
-        # Overflow from multiplication.
-        with self.assertRaises(OverflowError):
-            math.fma(a, b, 0.0)
-        self.assertEqual(math.fma(a, b/2.0, 0.0), c)
-        # Overflow from the addition.
-        with self.assertRaises(OverflowError):
-            math.fma(a, b/2.0, c)
-        # No overflow, even though a*b overflows a float.
-        self.assertEqual(math.fma(a, b, -c), c)
-
-        # Extreme case: a * b is exactly at the overflow boundary, so the
-        # tiniest offset makes a difference between overflow and a finite
-        # result.
-        a = float.fromhex('0x1.ffffffc000000p+511')
-        b = float.fromhex('0x1.0000002000000p+512')
-        c = float.fromhex('0x0.0000000000001p-1022')
-        with self.assertRaises(OverflowError):
-            math.fma(a, b, 0.0)
-        with self.assertRaises(OverflowError):
-            math.fma(a, b, c)
-        self.assertEqual(math.fma(a, b, -c),
-                         float.fromhex('0x1.fffffffffffffp+1023'))
-
-        # Another extreme case: here a*b is about as large as possible subject
-        # to math.fma(a, b, c) being finite.
-        a = float.fromhex('0x1.ae565943785f9p+512')
-        b = float.fromhex('0x1.3094665de9db8p+512')
-        c = float.fromhex('0x1.fffffffffffffp+1023')
-        self.assertEqual(math.fma(a, b, -c), c)
-
-    def test_fma_single_round(self):
-        a = float.fromhex('0x1p-50')
-        self.assertEqual(math.fma(a - 1.0, a + 1.0, 1.0), a*a)
-
-    def test_random(self):
-        # A collection of randomly generated inputs for which the naive FMA
-        # (with two rounds) gives a different result from a singly-rounded FMA.
-
-        # tuples (a, b, c, expected)
-        test_values = [
-            ('0x1.694adde428b44p-1', '0x1.371b0d64caed7p-1',
-             '0x1.f347e7b8deab8p-4', '0x1.19f10da56c8adp-1'),
-            ('0x1.605401ccc6ad6p-2', '0x1.ce3a40bf56640p-2',
-             '0x1.96e3bf7bf2e20p-2', '0x1.1af6d8aa83101p-1'),
-            ('0x1.e5abd653a67d4p-2', '0x1.a2e400209b3e6p-1',
-             '0x1.a90051422ce13p-1', '0x1.37d68cc8c0fbbp+0'),
-            ('0x1.f94e8efd54700p-2', '0x1.123065c812cebp-1',
-             '0x1.458f86fb6ccd0p-1', '0x1.ccdcee26a3ff3p-1'),
-            ('0x1.bd926f1eedc96p-1', '0x1.eee9ca68c5740p-1',
-             '0x1.960c703eb3298p-2', '0x1.3cdcfb4fdb007p+0'),
-            ('0x1.27348350fbccdp-1', '0x1.3b073914a53f1p-1',
-             '0x1.e300da5c2b4cbp-1', '0x1.4c51e9a3c4e29p+0'),
-            ('0x1.2774f00b3497bp-1', '0x1.7038ec336bff0p-2',
-             '0x1.2f6f2ccc3576bp-1', '0x1.99ad9f9c2688bp-1'),
-            ('0x1.51d5a99300e5cp-1', '0x1.5cd74abd445a1p-1',
-             '0x1.8880ab0bbe530p-1', '0x1.3756f96b91129p+0'),
-            ('0x1.73cb965b821b8p-2', '0x1.218fd3d8d5371p-1',
-             '0x1.d1ea966a1f758p-2', '0x1.5217b8fd90119p-1'),
-            ('0x1.4aa98e890b046p-1', '0x1.954d85dff1041p-1',
-             '0x1.122b59317ebdfp-1', '0x1.0bf644b340cc5p+0'),
-            ('0x1.e28f29e44750fp-1', '0x1.4bcc4fdcd18fep-1',
-             '0x1.fd47f81298259p-1', '0x1.9b000afbc9995p+0'),
-            ('0x1.d2e850717fe78p-3', '0x1.1dd7531c303afp-1',
-             '0x1.e0869746a2fc2p-2', '0x1.316df6eb26439p-1'),
-            ('0x1.cf89c75ee6fbap-2', '0x1.b23decdc66825p-1',
-             '0x1.3d1fe76ac6168p-1', '0x1.00d8ea4c12abbp+0'),
-            ('0x1.3265ae6f05572p-2', '0x1.16d7ec285f7a2p-1',
-             '0x1.0b8405b3827fbp-1', '0x1.5ef33c118a001p-1'),
-            ('0x1.c4d1bf55ec1a5p-1', '0x1.bc59618459e12p-2',
-             '0x1.ce5b73dc1773dp-1', '0x1.496cf6164f99bp+0'),
-            ('0x1.d350026ac3946p-1', '0x1.9a234e149a68cp-2',
-             '0x1.f5467b1911fd6p-2', '0x1.b5cee3225caa5p-1'),
-        ]
-        for a_hex, b_hex, c_hex, expected_hex in test_values:
-            a = float.fromhex(a_hex)
-            b = float.fromhex(b_hex)
-            c = float.fromhex(c_hex)
-            expected = float.fromhex(expected_hex)
-            self.assertEqual(math.fma(a, b, c), expected)
-            self.assertEqual(math.fma(b, a, c), expected)
-
-    # Custom assertions.
-    def assertIsNaN(self, value):
-        self.assertTrue(
-            math.isnan(value),
-            msg="Expected a NaN, got {!r}".format(value)
-        )
-
-    def assertIsPositiveZero(self, value):
-        self.assertTrue(
-            value == 0 and math.copysign(1, value) > 0,
-            msg="Expected a positive zero, got {!r}".format(value)
-        )
-
-    def assertIsNegativeZero(self, value):
-        self.assertTrue(
-            value == 0 and math.copysign(1, value) < 0,
-            msg="Expected a negative zero, got {!r}".format(value)
-        )
-
-
 def test_main():
     from doctest import DocFileSuite
     suite = unittest.TestSuite()
     suite.addTest(unittest.makeSuite(MathTests))
     suite.addTest(unittest.makeSuite(IsCloseTests))
-    suite.addTest(unittest.makeSuite(FMATests))
     suite.addTest(DocFileSuite("ieee754.txt"))
     run_unittest(suite)
 
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -215,9 +215,6 @@ Core and Builtins
 Library
 -------
 
-- Issue #29282: Added new math.fma function, wrapping C99's fma
-  operation.
-
 - Issue #29197: Removed deprecated function ntpath.splitunc().
 
 - Issue #29210: Removed support of deprecated argument "exclude" in
diff --git a/Modules/clinic/mathmodule.c.h b/Modules/clinic/mathmodule.c.h
@@ -80,40 +80,6 @@ PyDoc_STRVAR(math_factorial__doc__,
 #define MATH_FACTORIAL_METHODDEF    \
     {"factorial", (PyCFunction)math_factorial, METH_O, math_factorial__doc__},
 
-PyDoc_STRVAR(math_fma__doc__,
-"fma($module, x, y, z, /)\n"
-"--\n"
-"\n"
-"Fused multiply-add operation. Compute (x * y) + z with a single round.");
-
-#define MATH_FMA_METHODDEF    \
-    {"fma", (PyCFunction)math_fma, METH_FASTCALL, math_fma__doc__},
-
-static PyObject *
-math_fma_impl(PyObject *module, double x, double y, double z);
-
-static PyObject *
-math_fma(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwnames)
-{
-    PyObject *return_value = NULL;
-    double x;
-    double y;
-    double z;
-
-    if (!_PyArg_ParseStack(args, nargs, "ddd:fma",
-        &x, &y, &z)) {
-        goto exit;
-    }
-
-    if (!_PyArg_NoStackKeywords("fma", kwnames)) {
-        goto exit;
-    }
-    return_value = math_fma_impl(module, x, y, z);
-
-exit:
-    return return_value;
-}
-
 PyDoc_STRVAR(math_trunc__doc__,
 "trunc($module, x, /)\n"
 "--\n"
@@ -570,4 +536,4 @@ math_isclose(PyObject *module, PyObject **args, Py_ssize_t nargs, PyObject *kwna
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=f428e1075d00c334 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=71806f73a5c4bf0b input=a9049054013a1b77]*/
diff --git a/Modules/mathmodule.c b/Modules/mathmodule.c
