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1 dashley 25 /* $Header: /cvsroot/esrg/sfesrg/esrgpcpj/shared/c_datd/esrg_rand_int.c,v 1.4 2002/05/19 23:50:49 dtashley Exp $
2     **
3     ** A description of the functionality of this module and the public interface
4     ** definition is contained in the associated .H file.
5     */
6    
7     //--------------------------------------------------------------------------------
8     //Copyright 2001 David T. Ashley
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687     //-------------------------------------------------------------------------------------------------
688     //--------------------------------------------------------------------------------
689     #define MODULE_ESRG_RAND_INT
690    
691     #include <assert.h>
692     #include <string.h>
693     #include <time.h>
694    
695     #include "esrg_rand_int.h"
696     #include "intfunc.h"
697    
698    
699     void ESRG_RAND_INT_Alg01_Init(struct ESRG_RAND_INT_Alg01RngState *state,
700     int init_val)
701     {
702     int i;
703    
704     assert(state != NULL);
705     assert((init_val==-1) || (init_val>0));
706    
707     //Regardless of init type, zero out the structure. Among other things,
708     //this sets the number of remaining random bits to zero.
709     memset(state, 0, sizeof(*state));
710    
711     if (init_val == -1)
712     {
713     //This is the system randomness initialization case. Some value
714     //of system time should be adequate to start with.
715     state->rn_seed_whole = time(NULL);
716     state->rn_seed_fractional = time(NULL);
717    
718     //Flip a few bits in the seeds to hopefully make them different
719     //(but it doesn't matter if they aren't).
720     state->rn_seed_whole ^= 0xA5A5A5A5;
721     state->rn_seed_fractional ^= 0x5A5A5A5A;
722    
723     //Be absolutely sure that the seeds can't be zero.
724     state->rn_seed_whole |= 0x1;
725     state->rn_seed_fractional |= 0x2;
726    
727     //Iterate a small number of times to add further randomness
728     //to the two seeds.
729     for (i=0; i<3; i++)
730     {
731     state->rn_seed_whole
732     = INTFUNC_rn_power_res_16807_mapping(state->rn_seed_whole);
733     }
734    
735     for (i=0; i<7; i++)
736     {
737     state->rn_seed_fractional
738     = INTFUNC_rn_power_res_16807_mapping(state->rn_seed_fractional);
739     }
740     }
741     else
742     {
743     //This is the branch where the random seed is supplied. We can
744     //use very much the same approach as above to try to get something
745     //random.
746     state->rn_seed_whole = init_val;
747     state->rn_seed_fractional = init_val;
748    
749     //Flip a few bits in the seeds to hopefully make them different
750     //(but it doesn't matter if they aren't).
751     state->rn_seed_whole ^= 0xA5A5A5A5;
752     state->rn_seed_fractional ^= 0x5A5A5A5A;
753    
754     //Be absolutely sure that the seeds can't be zero.
755     state->rn_seed_whole |= 0x1;
756     state->rn_seed_fractional |= 0x2;
757    
758     //Iterate a small number of times to add further randomness
759     //to the two seeds.
760     for (i=0; i<3; i++)
761     {
762     state->rn_seed_whole
763     = INTFUNC_rn_power_res_16807_mapping(state->rn_seed_whole);
764     }
765    
766     for (i=0; i<7; i++)
767     {
768     state->rn_seed_fractional
769     = INTFUNC_rn_power_res_16807_mapping(state->rn_seed_fractional);
770     }
771     }
772    
773     //At this point the state is randomized. The number of bits valid
774     //in the bit reservoir is set to zero, so will force a restock
775     //next time.
776     }
777    
778    
779     //Restocks the bit reservoir.
780     static void ESRG_RAND_INT_Alg01_RestockBitBuffer(
781     struct ESRG_RAND_INT_Alg01RngState *state
782     )
783     {
784     assert(state != NULL);
785    
786     //We need to keep chugging along until we get an integer with the top two
787     //bits clear. This is the only way to get a random distribution of bits.
788     do
789     {
790     assert(state->rn_seed_fractional != 0);
791     state->rn_seed_fractional
792     = INTFUNC_rn_power_res_16807_mapping(state->rn_seed_fractional);
793     } while (state->rn_seed_fractional & 0xC0000000);
794    
795     //At this point the lower 30 bits should be random.
796     state->bit_buffer = state->rn_seed_fractional;
797     state->n_bb_valid = 30;
798     }
799    
800    
801     unsigned int ESRG_RAND_INT_Alg01_RandomBit(
802     struct ESRG_RAND_INT_Alg01RngState *state
803     )
804     {
805     int rv;
806    
807     assert(state != NULL);
808    
809     //Restock the supply of bits if necessary.
810     if (state->n_bb_valid == 0)
811     ESRG_RAND_INT_Alg01_RestockBitBuffer(state);
812    
813     if (state->bit_buffer & 0x01)
814     rv = 1;
815     else
816     rv = 0;
817    
818     state->bit_buffer >>= 1;
819     state->n_bb_valid--;
820    
821     return(rv);
822     }
823    
824    
825     unsigned int ESRG_RAND_INT_Alg01_RandomByte(
826     struct ESRG_RAND_INT_Alg01RngState *state
827     )
828     {
829     int rv;
830    
831     assert(state != NULL);
832    
833     //Be sure enough bits to yank a byte.
834     if (state->n_bb_valid < 8)
835     ESRG_RAND_INT_Alg01_RestockBitBuffer(state);
836    
837     //Grab the byte and return.
838     rv = state->bit_buffer & 0xFF;
839     state->bit_buffer >>= 8; //Must roll down to get new set of bits.
840     state->n_bb_valid -= 8;
841    
842     return(rv);
843     }
844    
845    
846     const char *ESRG_RAND_INT_cvcinfo(void)
847     {
848     return("$Header: /cvsroot/esrg/sfesrg/esrgpcpj/shared/c_datd/esrg_rand_int.c,v 1.4 2002/05/19 23:50:49 dtashley Exp $");
849     }
850    
851    
852     const char *ESRG_RAND_INT_hvcinfo(void)
853     {
854     return(ESRG_RAND_INT_H_VERSION);
855     }
856    
857    
858     /******************************************************************************
859     ** $Log: esrg_rand_int.c,v $
860     ** Revision 1.4 2002/05/19 23:50:49 dtashley
861     ** Minor bug corrected where same random byte would be supplied 3 times
862     ** in a row before new byte was supplied.
863     **
864     ** Revision 1.3 2002/05/15 21:59:22 dtashley
865     ** Checkin before .ZIP'ing up source code for assistance of newsgroup
866     ** posters.
867     **
868     ** Revision 1.2 2002/05/15 11:17:37 dtashley
869     ** Edits.
870     **
871     ** Revision 1.1 2002/05/15 09:00:57 dtashley
872     ** Initial checkin.
873     *******************************************************************************
874     ** End of ESRG_RAND_INT.C. */

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