/* $NetBSD: udivsi3.S,v 1.6 2020/04/23 03:12:49 rin 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 1.6 2020/04/23 03:12:49 rin Exp $")
#endif
#endif /* LIBC_SCCS and not lint */
| 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:
