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dnl AMD K6 mpn_rshift -- mpn right shift.
dnl Copyright 1999, 2000, 2002 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 K6: 3.0 cycles/limb
C mp_limb_t mpn_rshift (mp_ptr dst, mp_srcptr src, mp_size_t size,
C unsigned shift);
C
C The loop runs at 3 cycles/limb, limited by decoding and by having 3 mmx
C instructions. This is despite every second fetch being unaligned.
defframe(PARAM_SHIFT,16)
defframe(PARAM_SIZE, 12)
defframe(PARAM_SRC, 8)
defframe(PARAM_DST, 4)
deflit(`FRAME',0)
TEXT
ALIGN(32)
PROLOGUE(mpn_rshift)
deflit(`FRAME',0)
C The 1 limb case can be done without the push %ebx, but it's then
C still the same speed. The push is left as a free helping hand for
C the two_or_more code.
movl PARAM_SIZE, %eax
pushl %ebx FRAME_pushl()
movl PARAM_SRC, %ebx
decl %eax
movl PARAM_SHIFT, %ecx
jnz L(two_or_more)
movl (%ebx), %edx C src limb
movl PARAM_DST, %ebx
shrdl( %cl, %edx, %eax) C return value
shrl %cl, %edx
movl %edx, (%ebx) C dst limb
popl %ebx
ret
ALIGN(16) C avoid offset 0x1f
L(two_or_more):
C eax size-1
C ebx src
C ecx shift
C edx
movl (%ebx), %edx C src low limb
negl %ecx
addl $32, %ecx C 32-shift
movd PARAM_SHIFT, %mm6
shll %cl, %edx C retval
movl PARAM_DST, %ecx
leal (%ebx,%eax,4), %ebx
leal -4(%ecx,%eax,4), %ecx
negl %eax
L(simple):
C eax counter (negative)
C ebx &src[size-1]
C ecx &dst[size-1]
C edx retval
C
C mm0 scratch
C mm6 shift
Zdisp( movq, 0,(%ebx,%eax,4), %mm0)
incl %eax
psrlq %mm6, %mm0
Zdisp( movd, %mm0, 0,(%ecx,%eax,4))
jnz L(simple)
movq %mm0, (%ecx)
movl %edx, %eax
popl %ebx
emms
ret
EPILOGUE()
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