source/libs/gmp/gmp-src/mpn/arm/v6t2/gcd_1.asm

   1 dnl  ARM v6t2 mpn_gcd_1.
   2
   3 dnl  Based on the K7 gcd_1.asm, by Kevin Ryde.  Rehacked for ARM by Torbjörn
   4 dnl  Granlund.
   5
   6 dnl  Copyright 2000-2002, 2005, 2009, 2011, 2012 Free Software Foundation, Inc.
   7
   8 dnl  This file is part of the GNU MP Library.
   9 dnl
  10 dnl  The GNU MP Library is free software; you can redistribute it and/or modify
  11 dnl  it under the terms of either:
  12 dnl
  13 dnl    * the GNU Lesser General Public License as published by the Free
  14 dnl      Software Foundation; either version 3 of the License, or (at your
  15 dnl      option) any later version.
  16 dnl
  17 dnl  or
  18 dnl
  19 dnl    * the GNU General Public License as published by the Free Software
  20 dnl      Foundation; either version 2 of the License, or (at your option) any
  21 dnl      later version.
  22 dnl
  23 dnl  or both in parallel, as here.
  24 dnl
  25 dnl  The GNU MP Library is distributed in the hope that it will be useful, but
  26 dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  27 dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  28 dnl  for more details.
  29 dnl
  30 dnl  You should have received copies of the GNU General Public License and the
  31 dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
  32 dnl  see https://www.gnu.org/licenses/.
  33
  34 include(`../config.m4')
  35
  36 C            cycles/bit (approx)
  37 C StrongARM      -
  38 C XScale         -
  39 C Cortex-A7      ?
  40 C Cortex-A8      ?
  41 C Cortex-A9      5.3
  42 C Cortex-A15     3.5
  43 C Numbers measured with: speed -CD -s8-32 -t24 mpn_gcd_1
  44
  45 C TODO
  46 C  * Optimise inner-loop better.
  47 C  * Push saving/restoring of callee-user regs into call code
  48
  49 C Threshold of when to call bmod when U is one limb.  Should be about
  50 C (time_in_cycles(bmod_1,1) + call_overhead) / (cycles/bit).
  51 define(`BMOD_THRES_LOG2', 7)
  52
  53 C INPUT PARAMETERS
  54 define(`up',    `r0')
  55 define(`n',     `r1')
  56 define(`v0',    `r2')
  57
  58 ifdef(`BMOD_1_TO_MOD_1_THRESHOLD',,
  59   `define(`BMOD_1_TO_MOD_1_THRESHOLD',0xffffffff)')
  60
  61 ASM_START()
  62         TEXT
  63         ALIGN(16)
  64 PROLOGUE(mpn_gcd_1)
  65         push    {r4, r7, lr}
  66         ldr     r3, [up]        C U low limb
  67
  68         orr     r3, r3, v0
  69         rbit    r4, r3
  70         clz     r4, r4          C min(ctz(u0),ctz(v0))
  71
  72         rbit    r12, v0
  73         clz     r12, r12
  74         mov     v0, v0, lsr r12
  75
  76         mov     r7, v0
  77
  78         cmp     n, #1
  79         bne     L(nby1)
  80
  81 C Both U and V are single limbs, reduce with bmod if u0 >> v0.
  82         ldr     r3, [up]
  83         cmp     v0, r3, lsr #BMOD_THRES_LOG2
  84         bhi     L(red1)
  85
  86 L(bmod):mov     r3, #0          C carry argument
  87         bl      mpn_modexact_1c_odd
  88         b       L(red0)
  89
  90 L(nby1):cmp     n, #BMOD_1_TO_MOD_1_THRESHOLD
  91         blo     L(bmod)
  92
  93         bl      mpn_mod_1
  94
  95 L(red0):mov     r3, r0
  96 L(red1):cmp     r3, #0
  97         rbit    r12, r3
  98         clz     r12, r12
  99         bne     L(mid)
 100         b       L(end)
 101
 102         ALIGN(8)
 103 L(top): movcs   r3, r1          C if x-y < 0
 104         movcs   r7, r0          C use x,y-x
 105 L(mid): mov     r3, r3, lsr r12 C
 106         mov     r0, r3          C
 107         subs    r1, r7, r3      C
 108         rsb     r3, r7, r3      C
 109         rbit    r12, r1
 110         clz     r12, r12        C
 111         bne     L(top)          C
 112
 113 L(end): mov     r0, r7, lsl r4
 114         pop     {r4, r7, pc}
 115 EPILOGUE()