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Annotation of coherent/g/usr/lib/misc/randl.c, revision 1.1

1.1     ! root        1: /* fake version of ldiv() */
        !             2: typedef struct ldiv_t { long quot, rem; } ldiv_t;
        !             3: ldiv_t ldiv(numer, denom) long numer, denom;
        !             4: {
        !             5:        ldiv_t l;
        !             6:        l.quot = numer / denom;
        !             7:        l.rem = numer % denom;
        !             8:        return l;
        !             9: }
        !            10: /*-----------------------------------------------------------------*/
        !            11: /* Efficient and Portable Combined Random Number Generators */
        !            12: /* Pierre L'Ecuyer */
        !            13: /* CACM V. 31 N. 6 pp. 742-749, 774, June 1988 */
        !            14: 
        !            15: /* This random number generator has a period of 2e18. */
        !            16: /* It can be computed with 2 divides and 4 multiplies */
        !            17: /* where divides return 16 bit quotient and remainder */
        !            18: /* of a 32 bit number divided by a 16 bit number, and */
        !            19: /* mulitplies return a 32 bit product of two 16 bit */
        !            20: /* factors.  The ANSI portable implementation is less than */
        !            21: /* optimal, since it must be implemented using long arithmetic, */
        !            22: /* but at least the algorithm can be specified. */
        !            23: 
        !            24: static long s1 = 1;
        !            25: static long s2 = 1;
        !            26: 
        !            27: void srandl(seed1, seed2) unsigned long seed1, seed2;
        !            28: {
        !            29:        s1 = seed1 % 2147483562L + 1;
        !            30:        s2 = seed2 % 2147483398L + 1;
        !            31: }
        !            32: 
        !            33: /* uniform distribution in [1 .. 2147483562] */
        !            34: long randl()
        !            35: {
        !            36:        ldiv_t l;
        !            37:        register long t;
        !            38: 
        !            39:        l = ldiv(s1, 53668L);
        !            40:        if ((s1 = 40014L * l.rem - 12211 * l.quot) < 0)
        !            41:                s1 += 2147483563L;
        !            42:        l = ldiv(s2, 52774L);
        !            43:        if ((s2 = 40692L * l.rem - 3791 * l.quot) < 0)
        !            44:                s2 += 2147483399L;
        !            45:        if ((t = s1 - s2) < 1)
        !            46:                t += 2147483562L;
        !            47:        return t-1;
        !            48: }

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