1/* $NetBSD: udivsi3.S,v 1.6 2020/04/23 03:12:49 rin Exp $ */ 2 3/*- 4 * Copyright (c) 1990 The Regents of the University of California. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * the Systems Programming Group of the University of Utah Computer 9 * Science Department. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 */ 35 36#include <machine/asm.h> 37 38#if defined(LIBC_SCCS) && !defined(lint) 39#if 0 40 RCSID("from: @(#)udivsi3.s 5.1 (Berkeley) 6/7/90") 41#else 42 RCSID("$NetBSD: udivsi3.S,v 1.6 2020/04/23 03:12:49 rin Exp $") 43#endif 44#endif /* LIBC_SCCS and not lint */ 45 46/* unsigned / unsigned */ 47#ifndef __mc68010__ 48/* XXX sun3 need this for bootloader */ 49ENTRY(__udivsi3) 50 movel 4(%sp),%d0 51 divul 8(%sp),%d0 52 rts 53END(__udivsi3) 54#else 55ENTRY(__udivsi3) 56 movel %d2, -(%sp) | save %d2 57 movel 12(%sp), %d0 | load divisor 58 movel 8(%sp), %d1 | load dividend 59 60| first, we divide the divisor and dividend by two until 61| the divisor fits into 16 bits: 621: cmpil #0x10000, %d0 63 bcs 2f 64 lsrl #1, %d0 65 lsrl #1, %d1 66 bra 1b 672: 68 69| now we can do the divide. to avoid overflow, we have to 70| do the divide in two parts, high and low, and add the 71| results together: 72 movew %d1, %d2 | save low(dividend) 73 clrw %d1 74 swap %d1 | %d1 = dividend >> 16 75 divuw %d0, %d1 | do the high divide 76 moveal %d1, %a1 | save high divide result 77 movew %d2, %d1 | concat(remainder, low(dividend)) 78 divuw %d0, %d1 | do the low divide 79 movel %a1, %d0 | recover high divide result 80 swap %d0 81 clrw %d0 | %d0 = finished high divide result 82 andil #0xffff, %d1 | %d1 = finished low divide result 83 addl %d1, %d0 | %d0 = quotient guess 84 85| the quotient we have so far is only a guess. the divide we 86| did above was really the divide of some dividendB by some 87| divisorB, where the following hold: 88| 89| (dividend - divisor) <= dividendB <= dividend 90| (divisor / 2) < divisorB <= divisor 91| 92| so our guess quotient cannot be less than our real desired 93| quotient. however, it might be one too big. 94| 95| to adjust this quotient, we multiply it by the original 96| divisor and subtract the result from the original dividend. 97| if the result is nonnegative, our guessed quotient was 98| correct, and the subtraction result is our remainder. 99| if the result is negative, our guessed quotient was one 100| too big, and the subtraction result plus the original 101| divisor is our remainder. 102| 103| as in mulsi3, we have to do the multiply in stages to avoid 104| overflow: 105 106 movel 12(%sp), %d2 | load divisor 107 swap %d2 108 movel %d0, %d1 109 muluw %d2, %d1 | high(divisor) * low(guess) 110 moveal %d1, %a1 | save high(divisor) * low(guess) 111 swap %d2 112 movel %d0, %d1 113 swap %d1 114 muluw %d2, %d1 | low(divisor) * high(guess) 115 addl %a1, %d1 116 swap %d1 117 clrw %d1 | %d1 = finished high multiply result 118 moveal %d2, %a1 | save original divisor 119 muluw %d0, %d2 | low(guess) * low(divisor) 120 addl %d1, %d2 | %d2 = guess * divisor 121 122 movel 8(%sp), %d1 | load original dividend 123 subl %d2, %d1 | subtract 124 bcc 3f 125 subql #1, %d0 | adjust quotient 126 addl %a1, %d1 | adjust remainder 1273: movel (%sp)+, %d2 | restore %d2 128 rts 129END(__udivsi3) 130#endif /* __mc68010__ */ 131