prng/pmc31.d

   1 /* Invisible Vector Library
   2  * coded by Ketmar // Invisible Vector <ketmar@ketmar.no-ip.org>
   3  * Understanding is not required. Only obedience.
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, version 3 of the License ONLY.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  16  */
  17 // Park-Miller-Carta Pseudo-Random Number Generator, based on David G. Carta paper
  18 // 31 bit of randomness
  19 // seed is previous result, as usual
  20 module iv.prng.pmc31 /*is aliced*/;
  21 import iv.alice;
  22
  23
  24 struct PMC31 {
  25 private:
  26   enum si0 = 0x00aacc76u; //next step from 0x29au;
  27   uint s = si0;
  28
  29 public:
  30 pure nothrow @trusted @nogc:
  31   enum bool isUniformRandom = true;
  32   enum uint min = 0;
  33   enum uint max = 0x7fff_ffffu; // 31 bit
  34
  35   enum bool empty = false;
  36
  37   this (uint s0) { pragma(inline, true); seed(s0); }
  38
  39   @property uint front () const { pragma(inline, true); return s; }
  40
  41   auto save () const { pragma(inline, true); return PMC31(s); }
  42
  43   void popFront () {
  44     if (s == 0) s = si0;
  45     uint lo = 16807*(s&0xffff);
  46     immutable uint hi = 16807*(s>>16);
  47     lo += (hi&0x7fff)<<16;
  48     lo += hi>>15;
  49     //if (lo > 0x7fffffff) lo -= 0x7fffffff; // should be >=, actually
  50     s = (lo&0x7FFFFFFF)+(lo>>31); // same as previous code, but branch-less
  51   }
  52
  53   void seed (uint s0) { pragma(inline, true); s = (s0 ? s0 : si0); }
  54 }
  55
  56
  57 version(test_pmc31) unittest {
  58   static immutable uint[8] checkValues = [
  59     11193462u,
  60     1297438545u,
  61     500674177u,
  62     989963893u,
  63     1767336342u,
  64     1775578337u,
  65     712351247u,
  66     266076304u,
  67   ];
  68   {
  69     auto rng = PMC31(0);
  70     foreach (ulong v; checkValues) {
  71       if (v != rng.front) assert(0);
  72       //import std.stdio; writeln(rng.front, "u");
  73       rng.popFront();
  74     }
  75   }
  76   // std.random test
  77   {
  78     import std.random : uniform;
  79     auto rng = PMC31(0);
  80     foreach (immutable _; 0..8) {
  81       import std.stdio;
  82       auto v = uniform!"[)"(0, 4, rng);
  83       writeln(v, "uL");
  84     }
  85   }
  86 }