1File: rand.c                                                              Page       1
     1   /* rand.c - kluges a random number generator with addition & overflow */
     2   #include <portab.h>
     3    
     4    
     5   #define NSEEDS 7
     6    
     7   MLOCAL UWORD _seeds[NSEEDS] =
     8   	{ 0, 24213, 12345, 4622, 2143, 32010, 7942 };
     9    
    10   MLOCAL WORD _seedptr=0;
    11    
    12    
    13   WORD srand(seed1)
    14   	int seed1;
    15   {
    16   	WORD ncs;
    17   	_seeds[0] = seed1;
    18   	for( ncs = seed1&077; ncs; ncs-- )
    19   		rand();
    20   	return(rand());
    21   }
    22    
    23    
    24   WORD rand()
    25   {
    26   	UWORD tot, ii;
    27    
    28   	for( tot=0, ii=0; ii<NSEEDS; ii++)
    29   		tot += _seeds[ii];	/* ignore overflow */
    30   	if( ++_seedptr >= NSEEDS )
    31   		_seedptr = 0;
    32   	_seeds[_seedptr] = tot;
    33   	return( tot >> 1 );		/* ignore lo bit because of addition */
    34   }
    35