sys/kern/subr_rand.c

/*
 * Copyright (c) 1993 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the Computer Systems
 *      Engineering Group at Lawrence Berkeley Laboratory.
 * 4. Neither the name of the University nor of the Laboratory may be used
 *    to endorse or promote products derived from this software without
 *    specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * LBL BSD kernel random number generator (used by statclock).
 *
 * Written by Steve McCanne & Chris Torek (mccanne@ee.lbl.gov,
 * torek@ee.lbl.gov), November, 1992.
 *
 * This implementation is based on ``Two Fast Implementations of
 * the "Minimal Standard" Random Number Generator", David G. Carta,
 * Communications of the ACM, Jan 1990, Vol 33 No 1.
 */

#ifdef sparc
asm("\
        .global _kernrand                               ;\
_kernrand:                                              ;\
        sethi   %hi(16807), %o1                 ;\
        wr      %o1, %lo(16807), %y             ;\
        set     0xffff, %o4                     ;\
        andcc   %g0, 0, %o2                     ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %o0, %o2                   ;\
        mulscc  %o2, %g0, %o2                   ;\
        rd      %y, %o3                         ;\
        srl     %o2, 16, %o1                    ;\
        and     %o4, %o2, %o0                   ;\
        sll     %o0, 15, %o0                    ;\
        srl     %o3, 17, %o3                    ;\
        or      %o3, %o0, %o0                   ;\
        addcc   %o0, %o1, %o0                   ;\
        bl      1f                              ;\
         sethi  %hi(0x7fffffff), %o1            ;\
        retl                                    ;\
        nop                                     ;\
1:                                              ;\
        or      %o1, %lo(0x7fffffff), %o1       ;\
        add     %o0, 1, %o0                     ;\
        retl                                    ;\
        and     %o1, %o0, %o0                   ");
#else
long
kernrand(x)
        register long x;
{
        register long hi, lo, t;

        hi = x / 127773;
        lo = x % 127773;
        t = 16807 * lo - 2836 * hi;
        if (t > 0)
                return (t);
        else
                return (t + 0x7fffffff);
}
#endif