dnl PowerPC-32 mpn_mod_34lsub1 -- mpn remainder mod 2^24-1.
dnl Copyright 2002, 2003, 2005 Free Software Foundation, Inc.
dnl This file is part of the GNU MP Library.
dnl
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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.
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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
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include(`../config.m4')
C cycles/limb
C 603e: ?
C 604e: 3
C 75x (G3): 3
C 7400,7410 (G4): 3
C 744x,745x (G4+): 3
C power4/ppc970: 2.5
C power5: 2.5
C mp_limb_t mpn_mod_34lsub1 (mp_srcptr src, mp_size_t size)
C
C There seems no need to schedule the loads back, the code is still 3.0 c/l
C on 750/7400 no matter where they're placed.
C
C Alternatives:
C
C Fetching half words would allow add instead for accumulating, instead of
C adde and its serialization. An outer loop would be required though, since
C 2^16 halfwords can overflow. lhz+add would be 2.0 c/l, but if there's
C also a bdz or bdnz for each and a pointer update say every three limbs
C then the total would be 2.67 c/l which isn't much faster than the current
C simpler code.
ASM_START()
PROLOGUE(mpn_mod_34lsub1)
C r3 src
C r4 size
mtctr r4
addic r6, r3, 8 C &src[2], and clear CA
lwz r3, 0(r3) C acc0 = src[0]
bdz L(done)
lwz r4, -4(r6) C acc1 = src[1]
bdz L(two)
lwz r5, 0(r6) C acc2 = src[2]
lis r7, 0 C no carry if just three limbs
bdz L(three)
lis r7, 1 C 0x10000 carry pos
L(top):
C r3 acc0
C r4 acc1
C r5 acc2
C r6 src, incrementing
C r7 carry pos
lwz r0, 4(r6)
adde r3, r3, r0
bdz L(end0)
lwz r0, 8(r6)
adde r4, r4, r0
bdz L(end1)
lwzu r0, 12(r6)
adde r5, r5, r0
bdnz L(top)
srwi r7, r7, 8
L(end0):
srwi r7, r7, 8
L(end1):
subfe r0, r0, r0 C -1 if not CA
andc r7, r7, r0 C final carry, 0x10000, 0x100, 1 or 0
L(three):
rlwinm r6, r3, 0,8,31 C acc0 low
add r7, r7, r6
rlwinm r6, r3, 8,24,31 C acc0 high
add r7, r7, r6
rlwinm r6, r4, 8,8,23 C acc1 low
add r7, r7, r6
rlwinm r6, r4, 16,16,31 C acc1 high
add r7, r7, r6
rlwinm r6, r5, 16,8,15 C acc2 low
add r7, r7, r6
rlwinm r6, r5, 24,8,31 C acc2 high
add r3, r7, r6
L(done):
blr
L(two):
C r3 acc0
C r4 acc1
rlwinm r5, r3, 8,24,31 C acc0 high
rlwinm r3, r3, 0,8,31 C acc0 low
add r3, r3, r5 C acc0 high + low
rlwinm r5, r4, 16,16,31 C acc1 high
add r3, r3, r5 C add acc1 high
rlwinm r5, r4, 8,8,23 C acc1 low
add r3, r3, r5 C add acc1 low
blr
EPILOGUE()