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Annotation of sys/lib/libkern/arch/sparc64/random.S, Revision 1.1.1.1

1.1       nbrk        1: /*     $OpenBSD: random.S,v 1.2 2001/08/20 20:15:29 jason Exp $        */
                      2: /*     $NetBSD: random.S,v 1.1.1.1 1998/06/20 05:18:14 eeh Exp $       */
                      3:
                      4: /*
                      5:  * Copyright (c) 1990,1993 The Regents of the University of California.
                      6:  * All rights reserved.
                      7:  *
                      8:  * Redistribution and use in source and binary forms, with or without
                      9:  * modification, are permitted provided that: (1) source code distributions
                     10:  * retain the above copyright notice and this paragraph in its entirety, (2)
                     11:  * distributions including binary code include the above copyright notice and
                     12:  * this paragraph in its entirety in the documentation or other materials
                     13:  * provided with the distribution, and (3) all advertising materials mentioning
                     14:  * features or use of this software display the following acknowledgement:
                     15:  * ``This product includes software developed by the University of California,
                     16:  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
                     17:  * the University nor the names of its contributors may be used to endorse
                     18:  * or promote products derived from this software without specific prior
                     19:  * written permission.
                     20:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
                     21:  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
                     22:  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     23:  *
                     24:  * Here is a very good random number generator.  This implementation is
                     25:  * based on ``Two Fast Implementations of the "Minimal Standard" Random
                     26:  * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
                     27:  * Vol 33 No 1.  Do NOT modify this code unless you have a very thorough
                     28:  * understanding of the algorithm.  It's trickier than you think.  If
                     29:  * you do change it, make sure that its 10,000'th invocation returns
                     30:  * 1043618065.
                     31:  *
                     32:  * Here is easier-to-decipher pseudocode:
                     33:  *
                     34:  * p = (16807*seed)<30:0>      # e.g., the low 31 bits of the product
                     35:  * q = (16807*seed)<62:31>     # e.g., the high 31 bits starting at bit 32
                     36:  * if (p + q < 2^31)
                     37:  *     seed = p + q
                     38:  * else
                     39:  *     seed = ((p + q) & (2^31 - 1)) + 1
                     40:  * return (seed);
                     41:  *
                     42:  * The result is in (0,2^31), e.g., it's always positive.
                     43:  */
                     44: #include <machine/asm.h>
                     45:
                     46:        .data
                     47: randseed:
                     48:        .long   1
                     49:        .text
                     50: ENTRY(random)
                     51:        sethi   %hi(16807), %o1
                     52:        wr      %o1, %lo(16807), %y
                     53:         sethi  %hi(randseed), %g1
                     54:         ld     [%g1 + %lo(randseed)], %o0
                     55:         andcc  %g0, 0, %o2
                     56:        mulscc  %o2, %o0, %o2
                     57:        mulscc  %o2, %o0, %o2
                     58:        mulscc  %o2, %o0, %o2
                     59:        mulscc  %o2, %o0, %o2
                     60:        mulscc  %o2, %o0, %o2
                     61:        mulscc  %o2, %o0, %o2
                     62:        mulscc  %o2, %o0, %o2
                     63:        mulscc  %o2, %o0, %o2
                     64:        mulscc  %o2, %o0, %o2
                     65:        mulscc  %o2, %o0, %o2
                     66:        mulscc  %o2, %o0, %o2
                     67:        mulscc  %o2, %o0, %o2
                     68:        mulscc  %o2, %o0, %o2
                     69:        mulscc  %o2, %o0, %o2
                     70:        mulscc  %o2, %o0, %o2
                     71:        mulscc  %o2, %g0, %o2
                     72:        rd      %y, %o3
                     73:        srl     %o2, 16, %o1
                     74:        set     0xffff, %o4
                     75:        and     %o4, %o2, %o0
                     76:        sll     %o0, 15, %o0
                     77:        srl     %o3, 17, %o3
                     78:        or      %o3, %o0, %o0
                     79:        addcc   %o0, %o1, %o0
                     80:        bneg    1f
                     81:         sethi  %hi(0x7fffffff), %o1
                     82:        retl
                     83:         st     %o0, [%g1 + %lo(randseed)]
                     84: 1:
                     85:        or      %o1, %lo(0x7fffffff), %o1
                     86:        add     %o0, 1, %o0
                     87:        and     %o1, %o0, %o0
                     88:        retl
                     89:         st     %o0, [%g1 + %lo(randseed)]