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dnl PowerPC-32 mpn_divexact_by3 -- mpn by 3 exact division
dnl Copyright 2002, 2003, 2005, 2006 Free Software Foundation, Inc.
dnl
dnl This file is part of the GNU MP Library.
dnl
dnl The GNU MP Library is free software; you can redistribute it and/or
dnl modify it under the terms of the GNU Lesser General Public License as
dnl published by the Free Software Foundation; either version 2.1 of the
dnl License, or (at your option) any later version.
dnl
dnl The GNU MP Library is distributed in the hope that it will be useful,
dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
dnl Lesser General Public License for more details.
dnl
dnl You should have received a copy of the GNU Lesser General Public License
dnl along with the GNU MP Library; see the file COPYING.LIB. If not, write
dnl the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
dnl Boston, MA 02110-1301, USA.
include(`../config.m4')
C cycles/limb
C 603e: ?
C 604e: ?
C 75x (G3): ?
C 7400,7410 (G4): 8
C 744x,745x (G4+): 6
C power4/ppc970: 12
C power5: ?
C void mpn_divexact_by3 (mp_ptr dst, mp_srcptr src, mp_size_t size);
C
C We avoid the slow subfe instruction and instead rely on an extremely unlikely
C branch.
C
C The mullw has the inverse in the first operand, since 0xAA..AB won't allow
C any early-out. The src[] data normally won't either, but there's at least
C a chance, whereas 0xAA..AB never will. If, for instance, src[] is all
C zeros (not a sensible input of course) we run at 7.0 c/l on ppc750.
C
C The mulhwu has the "3" multiplier in the second operand, which lets 750 and
C 7400 use an early-out.
C INPUT PARAMETERS
define(`rp', `r3')
define(`up', `r4')
define(`n', `r5')
define(`cy', `r6')
ASM_START()
PROLOGUE(mpn_divexact_by3c)
lwz r11, 0(up)
mtctr n
lis r12, 0xAAAA
ori r12, r12, 0xAAAB
li r10, 3
cmplw cr7, cy, r11
subf r11, cy, r11
mullw r0, r11, r12
stw r0, 0(rp)
bdz L(one)
L(top): lwzu r9, 4(up)
mulhwu r7, r0, r10
bgt- cr7, L(adj) C very unlikely branch
L(bko): cmplw cr7, r7, r9
subf r0, r7, r9
mullw r0, r12, r0
stwu r0, 4(rp)
bdnz L(top)
L(one): mulhwu r3, r0, r10
blelr+ cr7
addi r3, r3, 1
blr
L(adj): addi r7, r7, 1
b L(bko)
EPILOGUE()
ASM_END()
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