Start a nep for cleaning the math configuration.

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+===========================================================
+Cleaning the math configuration of numpy.core
+===========================================================
+
+:Author: David Cournapeau
+:Contact: david@ar.media.kyoto-u.ac.jp
+:Date: 2008-09-04
+
+Executive summary
+=================
+
+Before building numpy.core, we use some configuration tests to gather some
+information about available math functions. Over the years, the configuration
+became convoluted, to the point it became difficult to support new platforms
+easily.
+
+The goal of this proposal is to clean the configuration of the math
+capabilities for easier maintenance.
+
+Current problems
+================
+
+Currently, the math configuration mainly test for some math functions, and
+configure numpy accordingly. But instead of testing each desired function
+independantly, the current system has been developed more as workarounds
+particular platform oddities, using platform implicit knowledge. This is
+against the normal philosophy of testing for capabilities only, which is the
+autoconf philosophy, which showed the path toward portability (on Unix at
+least) [1] This causes problems because modifying or adding configuration on
+existing platforms break the implicit assumption, without a clear solution.
+
+For example, on windows, when numpy is built with mingw, it would be nice to
+enforce the configuration sizeof(long double) == sizeof(double) because mingw
+uses the MS runtime, and the MS runtime does not support long double.
+Unfortunately, doing so breaks the mingw math function detection, because of
+the implicit assumption that mingw has a configuration sizeof(long double) !=
+sizeof(double).
+
+Another example is the testing for set of functions using only one function: if
+expf is found, it is assumed that all basic float functions are available.
+Instead, each function should be tested independantly (expf, sinf, etc...).
+
+Requirements
+============
+
+We have two strong requirements:
+	- it should not break any currently supported platform
+	- it should not make the configuration much slower (1-2 seconds are
+	  acceptable)
+
+Proposal
+========
+
+We suggest to break any implicit assumption, and test each math function
+independantly from each other, as usually done by autoconf. Since testing for a
+vast set of functions can be time consuming, we will use a scheme similar to
+AC_CHECK_FUNCS_ONCE in autoconf, that is test for a set of function at once,
+and only in the case it breaks, do the per function check. When the first check
+works, it should be as fast as the current scheme, except that the assumptions
+are explicitely checked (all functions implied by HAVE_LONGDOUBLE_FUNCS would
+be checked together, for example).
+
+License
+=======
+
+This document has been placed in the public domain.
+
+[1]: Autobook here