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rand_scs.c

00001 /*
00002  * Author  : Defour David
00003  * Contact : David.Defour@ens-lyon.fr
00004  *
00005  * This program is free software; you can redistribute it and/or modify
00006  * it under the terms of the GNU Lesser General Public License as published by
00007  * the Free Software Foundation; either version 2 of the License, or 
00008  * (at your option) any later version.
00009  * 
00010  * This program is distributed in the hope that it will be useful,
00011  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00012  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00013  * GNU General Public License for more details.
00014  *
00015  * You should have received a copy of the GNU Lesser General Public License
00016  * along with this program; if not, write to the Free Software
00017  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  
00018  */
00019 #include <stdlib.h>
00020 #include "scs.h"
00021 #include "scs_private.h"
00022 
00023 /*
00024  * Return 'sizeof(int)' random bits   
00025  */
00026 
00027 
00028 int rand_val(void){
00029   int val;
00030   int i;
00031 
00032   val = (rand() & 0x000000ff);
00033   for(i=0; i<(sizeof(int)); i++){
00034     val = val << 8;
00035     val += (rand() & 0x000000ff ); /* we keep only 8 bits */
00036   }
00037   return val;
00038 }
00039 
00040 
00041 /*
00042  * Put into 'result' a scs random number with the index field set
00043  * with a value between -expo_max and +expo_max.
00044  *
00045  * Rem. :
00046  * 1) If you want an scs number belonging to double precision floating
00047  * point number you must call scs_rand with an expo_max less than 39.
00048  * 2) expo_max must be less than RAND_MAX that is usually set a
00049  * value greater than 32767
00050  */
00051 void scs_rand(scs_ptr result, int expo_max){
00052   int i;
00053 
00054   R_EXP = 1;
00055   R_IND = (rand() % (2*expo_max)) - expo_max;
00056   R_SGN = ((2*rand()- RAND_MAX) > 0) ?  (-1) : (1);
00057 
00058   
00059   for(i=0; i<SCS_NB_WORDS; i++){
00060     /* We keep the first SCS_NB_BITS bits of a random value */
00061     R_HW[i] = rand_val() & SCS_MASK_RADIX; 
00062   }
00063 }

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