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.
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dnl The GNU MP Library is free software
; you can redistribute it and/or modify
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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.
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dnl The GNU MP Library is distributed in the hope that it will be useful, but
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; without even the implied warranty of MERCHANTABILITY
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or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General
Public License
dnl
for more details.
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dnl You should have received copies of the GNU General
Public License
and the
dnl GNU Lesser General
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If not,
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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()
