131 lines
2.9 KiB
NASM
131 lines
2.9 KiB
NASM
dnl AMD K7 mpn_divexact_by3 -- mpn division by 3, expecting no remainder.
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dnl Copyright 2000, 2002 Free Software Foundation, Inc.
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dnl
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dnl This file is part of the GNU MP Library.
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dnl
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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
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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
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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., 51 Franklin Street,
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dnl Fifth Floor, Boston, MA 02110-1301, USA.
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include(`../config.m4')
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C K7: 8.0 cycles/limb
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C mp_limb_t mpn_divexact_by3c (mp_ptr dst, mp_srcptr src, mp_size_t size,
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C mp_limb_t carry);
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defframe(PARAM_CARRY,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 multiplicative inverse of 3, modulo 2^32
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deflit(INVERSE_3, 0xAAAAAAAB)
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dnl ceil(b/3) and floor(b*2/3) where b=2^32
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deflit(ONE_THIRD_CEIL, 0x55555556)
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deflit(TWO_THIRDS_FLOOR, 0xAAAAAAAA)
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TEXT
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ALIGN(32)
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PROLOGUE(mpn_divexact_by3c)
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deflit(`FRAME',0)
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movl PARAM_SRC, %ecx
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pushl %ebx defframe_pushl(SAVE_EBX)
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movl PARAM_CARRY, %ebx
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pushl %ebp defframe_pushl(SAVE_EBP)
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movl PARAM_SIZE, %ebp
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pushl %edi defframe_pushl(SAVE_EDI)
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movl (%ecx), %eax C src low limb
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pushl %esi defframe_pushl(SAVE_ESI)
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movl PARAM_DST, %edi
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movl $TWO_THIRDS_FLOOR, %esi
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leal -4(%ecx,%ebp,4), %ecx C &src[size-1]
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subl %ebx, %eax
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setc %bl
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decl %ebp
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jz L(last)
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leal (%edi,%ebp,4), %edi C &dst[size-1]
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negl %ebp
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ALIGN(16)
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L(top):
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C eax src limb, carry subtracted
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C ebx carry limb (0 or 1)
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C ecx &src[size-1]
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C edx scratch
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C esi TWO_THIRDS_FLOOR
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C edi &dst[size-1]
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C ebp counter, limbs, negative
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imull $INVERSE_3, %eax, %edx
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movl 4(%ecx,%ebp,4), %eax C next src limb
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cmpl $ONE_THIRD_CEIL, %edx
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sbbl $-1, %ebx C +1 if result>=ceil(b/3)
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cmpl %edx, %esi
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sbbl %ebx, %eax C and further 1 if result>=ceil(b*2/3)
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movl %edx, (%edi,%ebp,4)
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incl %ebp
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setc %bl C new carry
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jnz L(top)
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L(last):
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C eax src limb, carry subtracted
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C ebx carry limb (0 or 1)
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C ecx &src[size-1]
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C edx scratch
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C esi multiplier
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C edi &dst[size-1]
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C ebp
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imull $INVERSE_3, %eax, %eax
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cmpl $ONE_THIRD_CEIL, %eax
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movl %eax, (%edi)
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movl SAVE_EBP, %ebp
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sbbl $-1, %ebx C +1 if eax>=ceil(b/3)
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cmpl %eax, %esi
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movl $0, %eax
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adcl %ebx, %eax C further +1 if eax>=ceil(b*2/3)
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movl SAVE_EDI, %edi
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movl SAVE_ESI, %esi
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movl SAVE_EBX, %ebx
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addl $FRAME, %esp
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ret
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EPILOGUE()
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