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dnl AMD64 mpn_lshsub_n. R = 2^k(U - V).
dnl Copyright 2006, 2011, 2012 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 cycles/limb
C AMD K8,K9 3.15 (mpn_sub_n + mpn_lshift costs about 4 c/l)
C AMD K10 3.15 (mpn_sub_n + mpn_lshift costs about 4 c/l)
C Intel P4 16.5
C Intel core2 4.35
C Intel corei ?
C Intel atom ?
C VIA nano ?
C This was written quickly and not optimized at all, but it runs very well on
C K8. But perhaps one could get under 3 c/l. Ideas:
C 1) Use indexing to save the 3 LEA
C 2) Write reasonable feed-in code
C 3) Be more clever about register usage
C 4) Unroll more, handling CL negation, carry save/restore cost much now
C 5) Reschedule
C INPUT PARAMETERS
define(`rp', `%rdi')
define(`up', `%rsi')
define(`vp', `%rdx')
define(`n', `%rcx')
define(`cnt', `%r8')
ABI_SUPPORT(DOS64)
ABI_SUPPORT(STD64)
ASM_START()
TEXT
ALIGN(16)
PROLOGUE(mpn_lshsub_n)
FUNC_ENTRY(4)
IFDOS(` mov 56(%rsp), %r8d ')
push %r12
push %r13
push %r14
push %r15
push %rbx
mov n, %rax
xor R32(%rbx), R32(%rbx) C clear carry save register
mov R32(%r8), R32(%rcx) C shift count
xor R32(%r15), R32(%r15) C limb carry
mov R32(%rax), R32(%r11)
and $3, R32(%r11)
je L(4)
sub $1, R32(%r11)
L(oopette):
add R32(%rbx), R32(%rbx) C restore carry flag
mov 0(up), %r8
lea 8(up), up
sbb 0(vp), %r8
mov %r8, %r12
sbb R32(%rbx), R32(%rbx) C save carry flag
shl R8(%rcx), %r8
or %r15, %r8
mov %r12, %r15
lea 8(vp), vp
neg R8(%rcx)
shr R8(%rcx), %r15
neg R8(%rcx)
mov %r8, 0(rp)
lea 8(rp), rp
sub $1, R32(%r11)
jnc L(oopette)
L(4):
sub $4, %rax
jc L(end)
ALIGN(16)
L(oop):
add R32(%rbx), R32(%rbx) C restore carry flag
mov 0(up), %r8
mov 8(up), %r9
mov 16(up), %r10
mov 24(up), %r11
lea 32(up), up
sbb 0(vp), %r8
mov %r8, %r12
sbb 8(vp), %r9
mov %r9, %r13
sbb 16(vp), %r10
mov %r10, %r14
sbb 24(vp), %r11
sbb R32(%rbx), R32(%rbx) C save carry flag
shl R8(%rcx), %r8
shl R8(%rcx), %r9
shl R8(%rcx), %r10
or %r15, %r8
mov %r11, %r15
shl R8(%rcx), %r11
lea 32(vp), vp
neg R8(%rcx)
shr R8(%rcx), %r12
shr R8(%rcx), %r13
shr R8(%rcx), %r14
shr R8(%rcx), %r15 C used next loop
or %r12, %r9
or %r13, %r10
or %r14, %r11
neg R8(%rcx)
mov %r8, 0(rp)
mov %r9, 8(rp)
mov %r10, 16(rp)
mov %r11, 24(rp)
lea 32(rp), rp
sub $4, %rax
jnc L(oop)
L(end):
neg R32(%rbx)
shl R8(%rcx), %rbx
adc %r15, %rbx
mov %rbx, %rax
pop %rbx
pop %r15
pop %r14
pop %r13
pop %r12
FUNC_EXIT()
ret
EPILOGUE()
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