Home | History | Annotate | Download | only in gallivm 
      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 
    102