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