/*      $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 */

/* unsigned / unsigned */
#ifndef __mc68010__
/* XXX sun3 need this for bootloader */
ENTRY(__udivsi3)
        movel   4(%sp),%d0
        divul   8(%sp),%d0
        rts
END(__udivsi3)
#else
ENTRY(__udivsi3)
        movel   %d2, -(%sp)     | save %d2
        movel   12(%sp), %d0    | load divisor
        movel   8(%sp), %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   12(%sp), %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   8(%sp), %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
END(__udivsi3)
#endif /* __mc68010__ */