/*      $NetBSD: random.S,v 1.6 2014/03/18 18:20:43 riastradh Exp $     */

/*
* Copyright (c) 1990,1993 The 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: (1) source code distributions
* retain the above copyright notice and this paragraph in its entirety, (2)
* distributions including binary code include the above copyright notice and
* this paragraph in its entirety in the documentation or other materials
* provided with the distribution, and (3) all advertising materials mentioning
* features or use of this software display the following acknowledgement:
* ``This product includes software developed by the University of California,
* Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
* the University nor the names of its contributors may be used to endorse
* or promote products derived from this software without specific prior
* written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* Here is a very good random number generator.  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.  Do NOT modify this code unless you have a very thorough
* understanding of the algorithm.  It's trickier than you think.  If
* you do change it, make sure that its 10,000'th invocation returns
* 1043618065.
*
* Here is easier-to-decipher pseudocode:
*
* p = (16807*seed)<30:0>       # e.g., the low 31 bits of the product
* q = (16807*seed)<62:31>      # e.g., the high 31 bits starting at bit 32
* if (p + q < 2^31)
*      seed = p + q
* else
*      seed = ((p + q) & (2^31 - 1)) + 1
* return (seed);
*
* The result is in (0,2^31), e.g., it's always positive.
*/
#include <machine/asm.h>

       .data
ASLOCAL(randseed)
       .long   1

ENTRY(random)
       movl    #16807, %d0
       LEA_LCL(_ASM_LABEL(randseed),%a0)
       mulsl   (%a0), %d1:%d0
       lsll    #1, %d0
       roxll   #2, %d1
       addl    %d1, %d0
       moveql  #1, %d1
       addxl   %d1, %d0
       lsrl    #1, %d0
       movl    %d0, (%a0)
       rts
END(random)