minix/common/lib/libc/arch/m68k/gen/udivsi3.S

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/* $NetBSD: udivsi3.S,v 1.2 2006/01/05 22:33:34 he Exp $ */
/*-
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* the Systems Programming Group of the University of Utah Computer
* Science Department.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <machine/asm.h>
#if defined(LIBC_SCCS) && !defined(lint)
#if 0
RCSID("from: @(#)udivsi3.s 5.1 (Berkeley) 6/7/90")
#else
RCSID("$NetBSD: udivsi3.S,v 1.2 2006/01/05 22:33:34 he Exp $")
#endif
#endif /* LIBC_SCCS and not lint */
/* unsigned / unsigned */
ENTRY(__udivsi3)
#ifndef __mc68010__
movel %sp@(4),%d0
divul %sp@(8),%d0
rts
#else
movel %d2, %sp@- | save %d2
movel %sp@(12), %d0 | load divisor
movel %sp@(8), %d1 | load dividend
| first, we divide the divisor and dividend by two until
| the divisor fits into 16 bits:
1: cmpil #0x10000, %d0
bcs 2f
lsrl #1, %d0
lsrl #1, %d1
bra 1b
2:
| now we can do the divide. to avoid overflow, we have to
| do the divide in two parts, high and low, and add the
| results together:
movew %d1, %d2 | save low(dividend)
clrw %d1
swap %d1 | %d1 = dividend >> 16
divuw %d0, %d1 | do the high divide
moveal %d1, %a1 | save high divide result
movew %d2, %d1 | concat(remainder, low(dividend))
divuw %d0, %d1 | do the low divide
movel %a1, %d0 | recover high divide result
swap %d0
clrw %d0 | %d0 = finished high divide result
andil #0xffff, %d1 | %d1 = finished low divide result
addl %d1, %d0 | %d0 = quotient guess
| the quotient we have so far is only a guess. the divide we
| did above was really the divide of some dividendB by some
| divisorB, where the following hold:
|
| (dividend - divisor) <= dividendB <= dividend
| (divisor / 2) < divisorB <= divisor
|
| so our guess quotient cannot be less than our real desired
| quotient. however, it might be one too big.
|
| to adjust this quotient, we multiply it by the original
| divisor and subtract the result from the original dividend.
| if the result is nonnegative, our guessed quotient was
| correct, and the subtraction result is our remainder.
| if the result is negative, our guessed quotient was one
| too big, and the subtraction result plus the original
| divisor is our remainder.
|
| as in mulsi3, we have to do the multiply in stages to avoid
| overflow:
movel %sp@(12), %d2 | load divisor
swap %d2
movel %d0, %d1
muluw %d2, %d1 | high(divisor) * low(guess)
moveal %d1, %a1 | save high(divisor) * low(guess)
swap %d2
movel %d0, %d1
swap %d1
muluw %d2, %d1 | low(divisor) * high(guess)
addl %a1, %d1
swap %d1
clrw %d1 | %d1 = finished high multiply result
moveal %d2, %a1 | save original divisor
muluw %d0, %d2 | low(guess) * low(divisor)
addl %d1, %d2 | %d2 = guess * divisor
movel %sp@(8), %d1 | load original dividend
subl %d2, %d1 | subtract
bcc 3f
subql #1, %d0 | adjust quotient
addl %a1, %d1 | adjust remainder
3: movel %sp@+, %d2 | restore %d2
rts
#endif /* __mc68010__ */