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random.S revision 1.3.32.1 
      1 /*	$NetBSD: random.S,v 1.3.32.1 2007/02/26 09:11:25 yamt Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1994 Ludd, University of Lule}, Sweden. All rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     11  * 2. Redistributions in binary form must reproduce the above copyright
     12  *    notice, this list of conditions and the following disclaimer in the
     13  *    documentation and/or other materials provided with the distribution.
     14  * 3. The name of the author may not be used to endorse or promote products
     15  *    derived from this software without specific prior written permission
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     18  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     19  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     20  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     21  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     22  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 /*
     30  * Copyright (c) 1990,1993 The Regents of the University of California.
     31  * All rights reserved.
     32  *
     33  * Redistribution and use in source and binary forms, with or without
     34  * modification, are permitted provided that: (1) source code distributions
     35  * retain the above copyright notice and this paragraph in its entirety, (2)
     36  * distributions including binary code include the above copyright notice and
     37  * this paragraph in its entirety in the documentation or other materials
     38  * provided with the distribution, and (3) all advertising materials mentioning
     39  * features or use of this software display the following acknowledgement:
     40  * ``This product includes software developed by the University of California,
     41  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
     42  * the University nor the names of its contributors may be used to endorse
     43  * or promote products derived from this software without specific prior
     44  * written permission.
     45  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
     46  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
     47  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
     48  *
     49  * Here is a very good random number generator.  This implementation is
     50  * based on ``Two Fast Implementations of the "Minimal Standard" Random
     51  * Number Generator'', David G. Carta, Communications of the ACM, Jan 1990,
     52  * Vol 33 No 1.  Do NOT modify this code unless you have a very thorough
     53  * understanding of the algorithm.  It's trickier than you think.  If
     54  * you do change it, make sure that its 10,000'th invocation returns
     55  * 1043618065.
     56  *
     57  * Here is easier-to-decipher pseudocode:
     58  *
     59  * p = (16807*seed)<30:0>	# e.g., the low 31 bits of the product
     60  * q = (16807*seed)<62:31>	# e.g., the high 31 bits starting at bit 32
     61  * if (p + q < 2^31)
     62  * 	seed = p + q
     63  * else
     64  *	seed = ((p + q) & (2^31 - 1)) + 1
     65  * return (seed);
     66  *
     67  * The result is in (0,2^31), e.g., it's always positive.
     68  */
     69 
     70 #include <machine/asm.h>
     71 
     72 	.data
     73 randseed:
     74 	.long	1
     75 
     76 ENTRY(random, 0)
     77 	movl	$16807,%r0
     78 
     79 	movl	randseed,%r1		# %r2=16807*loword(randseed)
     80 	bicl3	$0xffff0000,%r1,%r2
     81 	mull2	%r0,%r2
     82 	ashl	$-16,%r1,%r1		# %r1=16807*hiword(randseed)
     83 	bicl2	$0xffff0000,%r1
     84 	mull2	%r0,%r1
     85 	bicl3	$0xffff0000,%r2,%r0
     86 	ashl	$-16,%r2,%r2		# %r1+=(%r2>>16)
     87 	bicl2	$0xffff0000,%r2
     88 	addl2	%r2,%r1
     89 	ashl	$16,%r1,%r2		# %r0|=%r1<<16
     90 	bisl2	%r2,%r0
     91 	ashl	$-16,%r1,%r1		# %r1=%r1>>16
     92 
     93 	ashl	$1,%r1,%r1
     94 	movl	%r0,%r2
     95 	rotl	$1,%r0,%r0
     96 	bicl2	$0xfffffffe,%r0
     97 	bisl2	%r0,%r1
     98 	movl	%r2,%r0
     99 	bicl2	$0x80000000,%r0
    100 	addl2	%r1,%r0
    101 	bgeq	L1
    102 	subl2	$0x7fffffff,%r0
    103 L1:	movl	%r0,randseed
    104 	ret
    105