[boost] Optimized portable isnan, isfinite, fpclassify etc

From: Johan Råde (rade_at_[hidden])
Date: 2006-10-05 07:42:33

I have put together optimized implementations
of the following functions:

   template<class T> int fpclassify(T x);
   template<class T> bool isfinite(T x);
   template<class T> bool isinf(T x);
   template<class T> bool isnan(T x);
   template<class T> bool isnormal(T x);
   template<class T> bool signbit(T x);
   template<class T> T copysign(T x, T y);
   template<class T> T changesign(T x);

Here T is required to be float, double or long double.

--------------------

The code has been tested with

Windows / VC7.1 / i386
Mac / GCC 4.0 / powerpc
Linux / GCC 3.3 / i386, amd64, ia64, powerpc, mips, hppa

The code should work with most platforms
that support the IEEE754 standard.

--------------------

Many of these functions have also been
implemented by John Maddock.
The difference is that my implementation
is optimized for speed.

Here are some timing numbers on VC 7.1:

   float        Råde  Maddock  Native

   fpclassify     8      57       -
   isfinite       5      57       -
   isnormal       6      59       -
   isinf          5      57       -
   isnan          6      57       -

   double       Råde  Maddock  Native

   fpclassify    13      52      29
   isfinite      11      56      17
   isnormal      14      56       -
   isinf         10      52       -
   isnan          4      52      19

The times are in clock cycles for a single call,
based on an average of 10,000,000 calls
with random input.

--------------------

The code is available in the vault,
at "Home/Math - Numerics/fpclassify.zip".

Many thanks to Håkan Ardö who tested the code on Linux
and Olivier Verdie who tested the code on Mac.

--Johan Råde