arch/ia64/lib/carta_random.S

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Fast, simple, yet decent quality random number generator based on
   4  * a paper by David G. Carta ("Two Fast Implementations of the
   5  * `Minimal Standard' Random Number Generator," Communications of the
   6  * ACM, January, 1990).
   7  *
   8  * Copyright (C) 2002 Hewlett-Packard Co
   9  *      David Mosberger-Tang <davidm@hpl.hp.com>
  10  */
  11
  12 #include <asm/asmmacro.h>
  13
  14 #define a       r2
  15 #define m       r3
  16 #define lo      r8
  17 #define hi      r9
  18 #define t0      r16
  19 #define t1      r17
  20 #define seed    r32
  21
  22 GLOBAL_ENTRY(carta_random32)
  23         movl    a = (16807 << 16) | 16807
  24         ;;
  25         pmpyshr2.u t0 = a, seed, 0
  26         pmpyshr2.u t1 = a, seed, 16
  27         ;;
  28         unpack2.l t0 = t1, t0
  29         dep     m = -1, r0, 0, 31
  30         ;;
  31         zxt4    lo = t0
  32         shr.u   hi = t0, 32
  33         ;;
  34         dep     t0 = 0, hi, 15, 49      // t0 = (hi & 0x7fff)
  35         ;;
  36         shl     t0 = t0, 16             // t0 = (hi & 0x7fff) << 16
  37         shr     t1 = hi, 15             // t1 = (hi >> 15)
  38         ;;
  39         add     lo = lo, t0
  40         ;;
  41         cmp.gtu p6, p0 = lo, m
  42         ;;
  43 (p6)    and     lo = lo, m
  44         ;;
  45 (p6)    add     lo = 1, lo
  46         ;;
  47         add     lo = lo, t1
  48         ;;
  49         cmp.gtu p6, p0 = lo, m
  50         ;;
  51 (p6)    and     lo = lo, m
  52         ;;
  53 (p6)    add     lo = 1, lo
  54         br.ret.sptk.many rp
  55 END(carta_random32)