gcd_1.asm
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- dnl Alpha ev67 mpn_gcd_1 -- 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
- dnl modify it under the terms of the GNU Lesser General Public License as
- dnl published by the Free Software Foundation; either version 3 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. If not, see http://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.
- C
- C Enhancement:
- C
- C On the jsr, !lituse_jsr! (when available) would allow the linker to relax
- C it to a bsr, but probably only in a static binary. Plain "jsr foo" gives
- C the right object code for relaxation, and ought to be available
- C everywhere, but we prefer to schedule the GOT ldq (LEA) back earlier, for
- C the usual case of running in a shared library.
- C
- C bsr could perhaps be used explicitly anyway. We should be able to assume
- C modexact is in the same module as us (ie. shared library or mainline).
- C Would there be any worries about the size of the displacement? Could
- C always put modexact and gcd_1 in the same .o to be certain.
- ASM_START()
- PROLOGUE(mpn_gcd_1, gp)
- C r16 xp
- C r17 size
- C r18 y
- C ldah C l
- C lda C u
- ldq r0, 0(r16) C L x = xp[0]
- lda r30, -32(r30) C u alloc stack
- LEA( r27, mpn_modexact_1c_odd) C L modexact addr, ldq (gp)
- stq r10, 16(r30) C L save r10
- cttz r18, r10 C U0 y twos
- cmpeq r17, 1, r5 C u test size==1
- stq r9, 8(r30) C L save r9
- clr r19 C u zero c for modexact
- unop
- unop
- cttz r0, r6 C U0 x twos
- stq r26, 0(r30) C L save ra
- srl r18, r10, r18 C U y odd
- mov r18, r9 C l hold y across call
- cmpult r6, r10, r2 C u test x_twos < y_twos
- cmovne r2, r6, r10 C l common_twos = min(x_twos,y_twos)
- bne r5, L(one) C U no modexact if size==1
- jsr r26, (r27), mpn_modexact_1c_odd C L0
- LDGP( r29, 0(r26)) C u,l ldah,lda
- cttz r0, r6 C U0 new x twos
- ldq r26, 0(r30) C L restore ra
- L(one):
- mov r9, r1 C u y
- ldq r9, 8(r30) C L restore r9
- mov r10, r2 C u common twos
- ldq r10, 16(r30) C L restore r10
- lda r30, 32(r30) C l free stack
- beq r0, L(done) C U return y if x%y==0
- srl r0, r6, r0 C U x odd
- unop
- ALIGN(16)
- L(top):
- C r0 x
- C r1 y
- C r2 common twos, for use at end
- 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(done):
- sll r1, r2, r0 C U0 return y << common_twos
- ret r31, (r26), 1 C L0
- EPILOGUE()
- ASM_END()