src/gallium/auxiliary/gallivm/f.cpp

   1 /**************************************************************************
   2  *
   3  * (C) Copyright VMware, Inc 2010.
   4  * (C) Copyright John Maddock 2006.
   5  * Use, modification and distribution are subject to the
   6  * Boost Software License, Version 1.0. (See accompanying file
   7  * LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   8  *
   9  **************************************************************************/
  10
  11
  12 /*
  13  * This file allows to compute the minimax polynomial coefficients we use
  14  * for fast exp2/log2.
  15  *
  16  * How to use this source:
  17  *
  18  * - Download and abuild the NTL library from
  19  *   http://shoup.net/ntl/download.html
  20  *
  21  * - Download boost source code matching to your distro.
  22  *
  23  * - Goto libs/math/minimax and replace f.cpp with this file.
  24  *
  25  * - Build as
  26  *
  27  *   g++ -o minimax -I /path/to/ntl/include main.cpp f.cpp /path/to/ntl/src/ntl.a -lboost_math_tr1
  28  *
  29  * - Run as
  30  *
  31  *    ./minimax
  32  *
  33  * - For example, to compute exp2 5th order polynomial between [0, 1] do:
  34  *
  35  *    variant 1
  36  *    range 0 1
  37  *    order 5 0
  38  *    steps 200
  39  *    info
  40  *
  41  * - For more info see
  42  * http://www.boost.org/doc/libs/1_36_0/libs/math/doc/sf_and_dist/html/math_toolkit/toolkit/internals2/minimax.html
  43  */
  44
  45 #define L22
  46 #include <boost/math/bindings/rr.hpp>
  47 #include <boost/math/tools/polynomial.hpp>
  48
  49 #include <cmath>
  50
  51
  52 boost::math::ntl::RR f(const boost::math::ntl::RR& x, int variant)
  53 {
  54    static const boost::math::ntl::RR tiny = boost::math::tools::min_value<boost::math::ntl::RR>() * 64;
  55
  56    switch(variant)
  57    {
  58    case 0:
  59       // log2(x)/(x - 1)
  60       return log(x)/log(2.0)/(x - 1.0);
  61
  62    case 1:
  63       // exp2(x)
  64       return exp(x*log(2.0));
  65    }
  66
  67    return 0;
  68 }
  69
  70
  71 void show_extra(
  72    const boost::math::tools::polynomial<boost::math::ntl::RR>& n,
  73    const boost::math::tools::polynomial<boost::math::ntl::RR>& d,
  74    const boost::math::ntl::RR& x_offset,
  75    const boost::math::ntl::RR& y_offset,
  76    int variant)
  77 {
  78    switch(variant)
  79    {
  80    default:
  81       // do nothing here...
  82       ;
  83    }
  84 }
  85