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 build the NTL library from
  19  *   http://shoup.net/ntl/download.html , or install libntl-dev package if on
  20  *   Debian.
  21  *
  22  * - Download boost source code matching to your distro.
  23  *
  24  * - Goto libs/math/minimax and replace f.cpp with this file.
  25  *
  26  * - Build as
  27  *
  28  *   g++ -o minimax -I /path/to/ntl/include main.cpp f.cpp /path/to/ntl/src/ntl.a
  29  *
  30  * - Run as
  31  *
  32  *    ./minimax
  33  *
  34  * - For example, to compute exp2 5th order polynomial between [0, 1] do:
  35  *
  36  *    variant 0
  37  *    range 0 1
  38  *    order 5 0
  39  *    step 200
  40  *    info
  41  *
  42  *  and take the coefficients from the P = { ... } array.
  43  *
  44  * - To compute log2 4th order polynomial between [0, 1/9] do:
  45  *
  46  *    variant 1
  47  *    range 0 0.111111112
  48  *    order 4 0
  49  *    step 200
  50  *    info
  51  *
  52  * - For more info see
  53  * http://www.boost.org/doc/libs/1_47_0/libs/math/doc/sf_and_dist/html/math_toolkit/toolkit/internals2/minimax.html
  54  */
  55
  56 #define L22
  57 #include <boost/math/bindings/rr.hpp>
  58 #include <boost/math/tools/polynomial.hpp>
  59
  60 #include <cmath>
  61
  62 boost::math::ntl::RR exp2(const boost::math::ntl::RR& x)
  63 {
  64       return exp(x*log(2.0));
  65 }
  66
  67 boost::math::ntl::RR log2(const boost::math::ntl::RR& x)
  68 {
  69       return log(x)/log(2.0);
  70 }
  71
  72 boost::math::ntl::RR f(const boost::math::ntl::RR& x, int variant)
  73 {
  74    switch(variant)
  75    {
  76    case 0:
  77       return exp2(x);
  78
  79    case 1:
  80       return log2((1.0 + sqrt(x))/(1.0 - sqrt(x)))/sqrt(x);
  81    }
  82
  83    return 0;
  84 }
  85
  86
  87 void show_extra(
  88    const boost::math::tools::polynomial<boost::math::ntl::RR>& n,
  89    const boost::math::tools::polynomial<boost::math::ntl::RR>& d,
  90    const boost::math::ntl::RR& x_offset,
  91    const boost::math::ntl::RR& y_offset,
  92    int variant)
  93 {
  94    switch(variant)
  95    {
  96    default:
  97       // do nothing here...
  98       ;
  99    }
 100 }
 101