Merged revisions 65366 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r65366 | mark.dickinson | 2008-08-01 10:13:07 +0100 (Fri, 01 Aug 2008) | 2 lines
Tone down math.fsum warning.
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diff --git a/Doc/library/math.rst b/Doc/library/math.rst
index df4ec1b..da38305 100644
--- a/Doc/library/math.rst
+++ b/Doc/library/math.rst
@@ -85,29 +85,8 @@
.. note::
- On platforms where arithmetic results are not correctly rounded,
- :func:`fsum` may occasionally produce incorrect results; these
- results should be no less accurate than those from the builtin
- :func:`sum` function, but nevertheless may have arbitrarily
- large relative error.
-
- In particular, this affects some older Intel hardware (for
- example Pentium and earlier x86 processors) that makes use of
- 'extended precision' floating-point registers with 64 bits of
- precision instead of the 53 bits of precision provided by a C
- double. Arithmetic operations using these registers may be
- doubly rounded (rounded first to 64 bits, and then rerounded to
- 53 bits), leading to incorrectly rounded results. To test
- whether your machine is one of those affected, try the following
- at a Python prompt::
-
- >>> 1e16 + 2.9999
- 10000000000000002.0
-
- Machines subject to the double-rounding problem described above
- are likely to print ``10000000000000004.0`` instead of
- ``10000000000000002.0``.
-
+ The accuracy of fsum() may be impaired on builds that use
+ extended precision addition and then double-round the results.
.. versionadded:: 2.6