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dnl Alpha ev67 mpn_gcd_11 -- Nx1 greatest common divisor.
dnl Copyright 2003, 2004 Free Software Foundation, Inc.
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 modify
dnl it under the terms of either:
dnl
dnl * the GNU Lesser General Public License as published by the Free
dnl Software Foundation; either version 3 of the License, or (at your
dnl option) any later version.
dnl
dnl or
dnl
dnl * the GNU General Public License as published by the Free Software
dnl Foundation; either version 2 of the License, or (at your option) any
dnl later version.
dnl
dnl or both in parallel, as here.
dnl
dnl The GNU MP Library is distributed in the hope that it will be useful, but
dnl WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
dnl or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
dnl for more details.
dnl
dnl You should have received copies of the GNU General Public License and the
dnl GNU Lesser General Public License along with the GNU MP Library. If not,
dnl see https://www.gnu.org/licenses/.
include(`../config.m4')
C ev67: 3.4 cycles/bitpair for 1x1 part
C mp_limb_t mpn_gcd_1 (mp_srcptr xp, mp_size_t xsize, mp_limb_t y);
C
C In the 1x1 part, the algorithm is to change x,y to abs(x-y),min(x,y) and
C strip trailing zeros from abs(x-y) to maintain x and y both odd.
C
C The trailing zeros are calculated from just x-y, since in twos-complement
C there's the same number of trailing zeros on d or -d. This means the cttz
C runs in parallel with abs(x-y).
C
C The loop takes 5 cycles, and at 0.68 iterations per bit for two N-bit
C operands with this algorithm gives the measured 3.4 c/l.
C
C The slottings shown are for SVR4 style systems, Unicos differs in the
C initial gp setup and the LEA.
ASM_START()
PROLOGUE(mpn_gcd_11)
mov r16, r0
mov r17, r1
ALIGN(16)
L(top): subq r0, r1, r7 C l0 d = x - y
cmpult r0, r1, r16 C u0 test x >= y
subq r1, r0, r4 C l0 new_x = y - x
cttz r7, r8 C U0 d twos
cmoveq r16, r7, r4 C l0 new_x = d if x>=y
cmovne r16, r0, r1 C u0 y = x if x<y
unop C l \ force cmoveq into l0
unop C u /
C C cmoveq2 L0, cmovne2 U0
srl r4, r8, r0 C U0 x = new_x >> twos
bne r7, L(top) C U1 stop when d==0
L(end): mov r1, r0 C U0 return y << common_twos
ret r31, (r26), 1 C L0
EPILOGUE()
ASM_END()
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