arch/ia64/lib/carta_random.S

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