source/libs/gmp/gmp-src/mpn/x86/k6/mode1o.asm

   1 dnl  AMD K6 mpn_modexact_1_odd -- exact division style remainder.
   2
   3 dnl  Copyright 2000-2003, 2007 Free Software Foundation, Inc.
   4
   5 dnl  This file is part of the GNU MP Library.
   6 dnl
   7 dnl  The GNU MP Library is free software; you can redistribute it and/or modify
   8 dnl  it under the terms of either:
   9 dnl
  10 dnl    * the GNU Lesser General Public License as published by the Free
  11 dnl      Software Foundation; either version 3 of the License, or (at your
  12 dnl      option) any later version.
  13 dnl
  14 dnl  or
  15 dnl
  16 dnl    * the GNU General Public License as published by the Free Software
  17 dnl      Foundation; either version 2 of the License, or (at your option) any
  18 dnl      later version.
  19 dnl
  20 dnl  or both in parallel, as here.
  21 dnl
  22 dnl  The GNU MP Library is distributed in the hope that it will be useful, but
  23 dnl  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  24 dnl  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  25 dnl  for more details.
  26 dnl
  27 dnl  You should have received copies of the GNU General Public License and the
  28 dnl  GNU Lesser General Public License along with the GNU MP Library.  If not,
  29 dnl  see https://www.gnu.org/licenses/.
  30
  31 include(`../config.m4')
  32
  33
  34 C K6: 10.0 cycles/limb
  35
  36
  37 C mp_limb_t mpn_modexact_1_odd (mp_srcptr src, mp_size_t size,
  38 C                               mp_limb_t divisor);
  39 C mp_limb_t mpn_modexact_1c_odd (mp_srcptr src, mp_size_t size,
  40 C                                mp_limb_t divisor, mp_limb_t carry);
  41 C
  42 C A special case for high<divisor at the end measured only about 4 cycles
  43 C faster, and so isn't used.
  44 C
  45 C A special case for size==1 using a divl rather than the inverse measured
  46 C only about 5 cycles faster, and so isn't used.  When size==1 and
  47 C high<divisor it can skip a division and be a full 24 cycles faster, but
  48 C this isn't an important case.
  49
  50 defframe(PARAM_CARRY,  16)
  51 defframe(PARAM_DIVISOR,12)
  52 defframe(PARAM_SIZE,   8)
  53 defframe(PARAM_SRC,    4)
  54
  55         TEXT
  56
  57         ALIGN(32)
  58 PROLOGUE(mpn_modexact_1c_odd)
  59 deflit(`FRAME',0)
  60
  61         movl    PARAM_DIVISOR, %ecx
  62         pushl   %esi            FRAME_pushl()
  63
  64         movl    PARAM_CARRY, %edx
  65         jmp     L(start_1c)
  66
  67 EPILOGUE()
  68
  69
  70         ALIGN(16)
  71 PROLOGUE(mpn_modexact_1_odd)
  72 deflit(`FRAME',0)
  73
  74         movl    PARAM_DIVISOR, %ecx
  75         pushl   %esi            FRAME_pushl()
  76
  77         xorl    %edx, %edx
  78 L(start_1c):
  79         pushl   %edi            FRAME_pushl()
  80
  81         shrl    %ecx                    C d/2
  82         movl    PARAM_DIVISOR, %esi
  83
  84         andl    $127, %ecx              C d/2, 7 bits
  85         pushl   %ebp            FRAME_pushl()
  86
  87 ifdef(`PIC',`
  88         LEA(    binvert_limb_table, %edi)
  89 Zdisp(  movzbl, 0,(%ecx,%edi), %edi)            C inv 8 bits
  90 ',`
  91         movzbl  binvert_limb_table(%ecx), %edi  C inv 8 bits
  92 ')
  93         leal    (%edi,%edi), %ecx       C 2*inv
  94
  95         imull   %edi, %edi              C inv*inv
  96
  97         movl    PARAM_SRC, %eax
  98         movl    PARAM_SIZE, %ebp
  99
 100         imull   %esi, %edi              C inv*inv*d
 101
 102         pushl   %ebx            FRAME_pushl()
 103         leal    (%eax,%ebp,4), %ebx     C src end
 104
 105         subl    %edi, %ecx              C inv = 2*inv - inv*inv*d
 106         leal    (%ecx,%ecx), %edi       C 2*inv
 107
 108         imull   %ecx, %ecx              C inv*inv
 109
 110         movl    (%eax), %eax            C src low limb
 111         negl    %ebp                    C -size
 112
 113         imull   %esi, %ecx              C inv*inv*d
 114
 115         subl    %ecx, %edi              C inv = 2*inv - inv*inv*d
 116
 117         ASSERT(e,`      C d*inv == 1 mod 2^GMP_LIMB_BITS
 118         pushl   %eax
 119         movl    %esi, %eax
 120         imull   %edi, %eax
 121         cmpl    $1, %eax
 122         popl    %eax')
 123
 124         jmp     L(entry)
 125
 126
 127 C Rotating the mul to the top of the loop saves 1 cycle, presumably by
 128 C hiding the loop control under the imul latency.
 129 C
 130 C The run time is 10 cycles, but decoding is only 9 (and the dependent chain
 131 C only 8).  It's not clear how to get down to 9 cycles.
 132 C
 133 C The xor and rcl to handle the carry bit could be an sbb instead, with the
 134 C the carry bit add becoming a sub, but that doesn't save anything.
 135
 136 L(top):
 137         C eax   (low product)
 138         C ebx   src end
 139         C ecx   carry bit, 0 or 1
 140         C edx   (high product, being carry limb)
 141         C esi   divisor
 142         C edi   inverse
 143         C ebp   counter, limbs, negative
 144
 145         mull    %esi
 146
 147         movl    (%ebx,%ebp,4), %eax
 148         addl    %ecx, %edx              C apply carry bit to carry limb
 149
 150 L(entry):
 151         xorl    %ecx, %ecx
 152         subl    %edx, %eax              C apply carry limb
 153
 154         rcll    %ecx
 155
 156         imull   %edi, %eax
 157
 158         incl    %ebp
 159         jnz     L(top)
 160
 161
 162
 163         popl    %ebx
 164         popl    %ebp
 165
 166         mull    %esi
 167
 168         popl    %edi
 169         popl    %esi
 170
 171         leal    (%ecx,%edx), %eax
 172
 173         ret
 174
 175 EPILOGUE()
 176 ASM_END()