1/* $NetBSD: udivsi3.S,v 1.2 2006/01/05 22:33:34 he 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 1.2 2006/01/05 22:33:34 he Exp $") 43#endif 44#endif /* LIBC_SCCS and not lint */ 45 46/* unsigned / unsigned */ 47ENTRY(__udivsi3) 48#ifndef __mc68010__ 49 movel %sp@(4),%d0 50 divul %sp@(8),%d0 51 rts 52#else 53 movel %d2, %sp@- | save %d2 54 movel %sp@(12), %d0 | load divisor 55 movel %sp@(8), %d1 | load dividend 56 57| first, we divide the divisor and dividend by two until 58| the divisor fits into 16 bits: 591: cmpil #0x10000, %d0 60 bcs 2f 61 lsrl #1, %d0 62 lsrl #1, %d1 63 bra 1b 642: 65 66| now we can do the divide. to avoid overflow, we have to 67| do the divide in two parts, high and low, and add the 68| results together: 69 movew %d1, %d2 | save low(dividend) 70 clrw %d1 71 swap %d1 | %d1 = dividend >> 16 72 divuw %d0, %d1 | do the high divide 73 moveal %d1, %a1 | save high divide result 74 movew %d2, %d1 | concat(remainder, low(dividend)) 75 divuw %d0, %d1 | do the low divide 76 movel %a1, %d0 | recover high divide result 77 swap %d0 78 clrw %d0 | %d0 = finished high divide result 79 andil #0xffff, %d1 | %d1 = finished low divide result 80 addl %d1, %d0 | %d0 = quotient guess 81 82| the quotient we have so far is only a guess. the divide we 83| did above was really the divide of some dividendB by some 84| divisorB, where the following hold: 85| 86| (dividend - divisor) <= dividendB <= dividend 87| (divisor / 2) < divisorB <= divisor 88| 89| so our guess quotient cannot be less than our real desired 90| quotient. however, it might be one too big. 91| 92| to adjust this quotient, we multiply it by the original 93| divisor and subtract the result from the original dividend. 94| if the result is nonnegative, our guessed quotient was 95| correct, and the subtraction result is our remainder. 96| if the result is negative, our guessed quotient was one 97| too big, and the subtraction result plus the original 98| divisor is our remainder. 99| 100| as in mulsi3, we have to do the multiply in stages to avoid 101| overflow: 102 103 movel %sp@(12), %d2 | load divisor 104 swap %d2 105 movel %d0, %d1 106 muluw %d2, %d1 | high(divisor) * low(guess) 107 moveal %d1, %a1 | save high(divisor) * low(guess) 108 swap %d2 109 movel %d0, %d1 110 swap %d1 111 muluw %d2, %d1 | low(divisor) * high(guess) 112 addl %a1, %d1 113 swap %d1 114 clrw %d1 | %d1 = finished high multiply result 115 moveal %d2, %a1 | save original divisor 116 muluw %d0, %d2 | low(guess) * low(divisor) 117 addl %d1, %d2 | %d2 = guess * divisor 118 119 movel %sp@(8), %d1 | load original dividend 120 subl %d2, %d1 | subtract 121 bcc 3f 122 subql #1, %d0 | adjust quotient 123 addl %a1, %d1 | adjust remainder 1243: movel %sp@+, %d2 | restore %d2 125 rts 126#endif /* __mc68010__ */ 127