Distributed-Run-Time-Resource-Manager/RCCE_V2.0/apps/NPB/common/randdp.c

// 
// Copyright 2010 Intel Corporation
// 
//    Licensed under the Apache License, Version 2.0 (the "License");
//    you may not use this file except in compliance with the License.
//    You may obtain a copy of the License at
// 
//        http://www.apache.org/licenses/LICENSE-2.0
// 
//    Unless required by applicable law or agreed to in writing, software
//    distributed under the License is distributed on an "AS IS" BASIS,
//    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//    See the License for the specific language governing permissions and
//    limitations under the License.
// 
//---------------------------------------------------------------------
//   This function is C verson of random number generator randdp.f 
//---------------------------------------------------------------------

double	randlc(X, A)
double *X;
double *A;
{
      static int        KS=0;
      static double	R23, R46, T23, T46;
      double		T1, T2, T3, T4;
      double		A1;
      double		A2;
      double		X1;
      double		X2;
      double		Z;
      int     		i, j;

      if (KS == 0) 
      {
        R23 = 1.0;
        R46 = 1.0;
        T23 = 1.0;
        T46 = 1.0;
    
        for (i=1; i<=23; i++)
        {
          R23 = 0.50 * R23;
          T23 = 2.0 * T23;
        }
        for (i=1; i<=46; i++)
        {
          R46 = 0.50 * R46;
          T46 = 2.0 * T46;
        }
        KS = 1;
      }

/*  Break A into two parts such that A = 2^23 * A1 + A2 and set X = N.  */

      T1 = R23 * *A;
      j  = T1;
      A1 = j;
      A2 = *A - T23 * A1;

/*  Break X into two parts such that X = 2^23 * X1 + X2, compute
    Z = A1 * X2 + A2 * X1  (mod 2^23), and then
    X = 2^23 * Z + A2 * X2  (mod 2^46).                            */

      T1 = R23 * *X;
      j  = T1;
      X1 = j;
      X2 = *X - T23 * X1;
      T1 = A1 * X2 + A2 * X1;
      
      j  = R23 * T1;
      T2 = j;
      Z = T1 - T23 * T2;
      T3 = T23 * Z + A2 * X2;
      j  = R46 * T3;
      T4 = j;
      *X = T3 - T46 * T4;
      return(R46 * *X);
}