119 lines
4.4 KiB
ArmAsm
119 lines
4.4 KiB
ArmAsm
/* $NetBSD: udivsi3.S,v 1.1 2002/03/26 22:49:33 fredette Exp $ */
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/*-
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* Copyright (c) 2002 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Matthew Fredette.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the NetBSD
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* Foundation, Inc. and its contributors.
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* 4. Neither the name of The NetBSD Foundation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <machine/asm.h>
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#if defined(LIBC_SCCS) && !defined(lint)
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RCSID("$NetBSD: udivsi3.S,v 1.1 2002/03/26 22:49:33 fredette Exp $");
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#endif /* LIBC_SCCS and not lint */
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ENTRY(__udivsi3)
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movel %d2, %sp@- | save %d2
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movel %sp@(12), %d0 | load divisor
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movel %sp@(8), %d1 | load dividend
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| first, we divide the divisor and dividend by two until
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| the divisor fits into 16 bits:
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1: cmpil #0x10000, %d0
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bcs 2f
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lsrl #1, %d0
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lsrl #1, %d1
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bra 1b
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2:
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| now we can do the divide. to avoid overflow, we have to
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| do the divide in two parts, high and low, and add the
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| results together:
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movew %d1, %d2 | save low(dividend)
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clrw %d1
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swap %d1 | %d1 = dividend >> 16
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divuw %d0, %d1 | do the high divide
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moveal %d1, %a1 | save high divide result
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movew %d2, %d1 | concat(remainder, low(dividend))
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divuw %d0, %d1 | do the low divide
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movel %a1, %d0 | recover high divide result
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swap %d0
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clrw %d0 | %d0 = finished high divide result
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andil #0xffff, %d1 | %d1 = finished low divide result
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addl %d1, %d0 | %d0 = quotient guess
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| the quotient we have so far is only a guess. the divide we
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| did above was really the divide of some dividendB by some
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| divisorB, where the following hold:
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| (dividend - divisor) <= dividendB <= dividend
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| (divisor / 2) < divisorB <= divisor
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| so our guess quotient cannot be less than our real desired
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| quotient. however, it might be one too big.
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| to adjust this quotient, we multiply it by the original
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| divisor and subtract the result from the original dividend.
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| if the result is nonnegative, our guessed quotient was
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| correct, and the subtraction result is our remainder.
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| if the result is negative, our guessed quotient was one
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| too big, and the subtraction result plus the original
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| divisor is our remainder.
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| as in mulsi3, we have to do the multiply in stages to avoid
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| overflow:
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movel %sp@(12), %d2 | load divisor
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swap %d2
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movel %d0, %d1
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muluw %d2, %d1 | high(divisor) * low(guess)
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moveal %d1, %a1 | save high(divisor) * low(guess)
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swap %d2
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movel %d0, %d1
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swap %d1
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muluw %d2, %d1 | low(divisor) * high(guess)
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addl %a1, %d1
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swap %d1
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clrw %d1 | %d1 = finished high multiply result
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moveal %d2, %a1 | save original divisor
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muluw %d0, %d2 | low(guess) * low(divisor)
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addl %d1, %d2 | %d2 = guess * divisor
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movel %sp@(8), %d1 | load original dividend
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subl %d2, %d1 | subtract
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bcc 3f
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subql #1, %d0 | adjust quotient
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addl %a1, %d1 | adjust remainder
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3: movel %sp@+, %d2 | restore %d2
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rts
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