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dnl AMD K6-2 mpn_rshift -- mpn right shift.
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dnl K6-2: 1.75 cycles/limb
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dnl Copyright (C) 1999, 2000 Free Software Foundation, Inc.
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dnl This file is part of the GNU MP Library.
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dnl The GNU MP Library is free software; you can redistribute it and/or
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dnl modify it under the terms of the GNU Lesser General Public License as
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dnl published by the Free Software Foundation; either version 2.1 of the
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dnl License, or (at your option) any later version.
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dnl The GNU MP Library is distributed in the hope that it will be useful,
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dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
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dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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dnl Lesser General Public License for more details.
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dnl You should have received a copy of the GNU Lesser General Public
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dnl License along with the GNU MP Library; see the file COPYING.LIB. If
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dnl not, write to the Free Software Foundation, Inc., 59 Temple Place -
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dnl Suite 330, Boston, MA 02111-1307, USA.
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include(`../config.m4')
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C mp_limb_t mpn_rshift (mp_ptr dst, mp_srcptr src, mp_size_t size,
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defframe(PARAM_SHIFT,16)
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defframe(PARAM_SIZE, 12)
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defframe(PARAM_SRC, 8)
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defframe(PARAM_DST, 4)
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dnl Minimum 9, because the unrolled loop can't handle less.
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deflit(UNROLL_THRESHOLD, 9)
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C The 1 limb case can be done without the push %ebx, but it's then
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C still the same speed. The push is left as a free helping hand for
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C the two_or_more code.
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pushl %ebx FRAME_pushl()
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movl PARAM_SHIFT, %ecx
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movl (%ebx), %edx C src limb
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shrdl( %cl, %edx, %eax) C return value
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movl %edx, (%ebx) C dst limb
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C -----------------------------------------------------------------------------
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ALIGN(16) C avoid offset 0x1f
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movl (%ebx), %edx C src low limb
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movd PARAM_SHIFT, %mm6
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cmpl $UNROLL_THRESHOLD-1, %eax
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leal (%ebx,%eax,4), %ebx
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leal -4(%ecx,%eax,4), %ecx
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C This loop runs at about 3 cycles/limb, which is the amount of
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C decoding, and this is despite every second access being unaligned.
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C eax counter, -(size-1) to -1
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Zdisp( movq, 0,(%ebx,%eax,4), %mm0)
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Zdisp( movd, %mm0, 0,(%ecx,%eax,4))
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C -----------------------------------------------------------------------------
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subl $7, %eax C size-8
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movq (%ebx), %mm2 C src low qword
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leal (%ebx,%eax,4), %ebx C src end - 32
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leal (%ecx,%eax,4), %ecx C dst end - 32
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notl %eax C -(size-7)
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Zdisp( movd, %mm2, 0,(%ecx,%eax,4)) C dst low limb
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movq 4(%ebx,%eax,4), %mm2 C new src low qword
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movq 12(%ebx,%eax,4), %mm0 C src second lowest qword
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nop C avoid bad cache line crossing
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C This loop is the important bit, the rest is just support for it.
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C Four src limbs are held at the start, and four more will be read.
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C Four dst limbs will be written. This schedule seems necessary for
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C The use of -(size-7) lets the loop stop when %eax becomes >= 0 and
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C and leaves 0 to 3 which can be tested with test $1 and $2.
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C eax counter, -(size-7) step by +4 until >=0
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movq 4(%ebx,%eax,4), %mm0
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movq %mm2, -12(%ecx,%eax,4)
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movq 12(%ebx,%eax,4), %mm0
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movq %mm1, -4(%ecx,%eax,4)
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ja L(top) C jump if no carry and not zero
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C Now have the four limbs in mm2 (low) and mm0 (high), and %eax is 0
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C to 3 representing respectively 3 to 0 further limbs.
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testl $2, %eax C testl to avoid bad cache line crossings
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C Two or three extra limbs: rshift mm2, OR it with lshifted mm0, mm0
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C becomes new mm2 and a new mm0 is loaded.
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movq 12(%ebx,%eax,4), %mm0
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movq %mm2, -4(%ecx,%eax,4)
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movq %mm2, 4(%ecx,%eax,4)
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C one further extra limb to process
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movd 32-4(%ebx), %mm0 C src[size-1], most significant limb
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movq %mm1, 32-12(%ecx) C dst[size-3,size-2]
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movd %mm2, 32-4(%ecx) C dst[size-1]
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movl %edx, %eax C retval
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nop C avoid bad cache line crossing
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C no further extra limbs
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movq %mm1, 32-8(%ecx) C dst[size-2,size-1]
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movl %edx, %eax C retval
added
removed
gmp/mpn/x86/k6/k62mmx/rshift.asm
