/* $OpenBSD: sdiv.S,v 1.1 2007/11/25 18:25:36 deraadt Exp $ */ /* $NetBSD: divrem.m4,v 1.3 1995/04/22 09:37:39 pk Exp $ */ /* * Copyright (c) 1992, 1993 * The Regents of the University of California. All rights reserved. * * This software was developed by the Computer Systems Engineering group * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and * contributed to Berkeley. * * 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. * * Header: divrem.m4,v 1.4 92/06/25 13:23:57 torek Exp */ /* * Division and remainder, from Appendix E of the Sparc Version 8 * Architecture Manual, with fixes from Gordon Irlam. */ /* * Input: dividend and divisor in %o0 and %o1 respectively. * * m4 parameters: * .div name of function to generate * _C_LABEL(_div) secondary name of function to generate * div div=div => %o0 / %o1; div=rem => %o0 % %o1 * true true=true => signed; true=false => unsigned * * Algorithm parameters: * N how many bits per iteration we try to get (4) * WORDSIZE total number of bits (32) * * Derived constants: * TWOSUPN 2^N, for label generation (m4 exponentiation currently broken) * TOPBITS number of bits in the top decade of a number * * Important variables: * Q the partial quotient under development (initially 0) * R the remainder so far, initially the dividend * ITER number of main division loop iterations required; * equal to ceil(log2(quotient) / N). Note that this * is the log base (2^N) of the quotient. * V the current comparand, initially divisor*2^(ITER*N-1) * * Cost: * Current estimate for non-large dividend is * ceil(log2(quotient) / N) * (10 + 7N/2) + C * A large dividend is one greater than 2^(31-TOPBITS) and takes a * different path, as the upper bits of the quotient must be developed * one bit at a time. */ /* m4 reminder: d => if a is b, then c, else d */ /* * This is the recursive definition for developing quotient digits. * * Parameters: * $1 the current depth, 1 <= $1 <= 4 * $2 the current accumulation of quotient bits * 4 max depth * * We add a new bit to $2 and either recurse or insert the bits in * the quotient. %o3, %o2, and %o5 are inputs and outputs as defined above; * the condition codes are expected to reflect the input %o3, and are * modified to reflect the output %o3. */ #include "DEFS.h" #include #include .globl _C_LABEL(_div) _C_LABEL(_div): FUNC(.div) ! compute sign of result; if neither is negative, no problem orcc %o1, %o0, %g0 ! either negative? bge 2f ! no, go do the divide xor %o1, %o0, %g6 ! compute sign in any case tst %o1 bge 1f tst %o0 ! %o1 is definitely negative; %o0 might also be negative bge 2f ! if %o0 not negative... neg %o1 ! in any case, make %o1 nonneg 1: ! %o0 is negative, %o1 is nonnegative neg %o0 ! make %o0 nonnegative 2: ! Ready to divide. Compute size of quotient; scale comparand. orcc %o1, %g0, %o5 bnz 1f mov %o0, %o3 ! Divide by zero trap. If it returns, return 0 (about as ! wrong as possible, but that is what SunOS does...). t ST_DIV0 retl clr %o0 1: cmp %o3, %o5 ! if %o1 exceeds %o0, done blu Lgot_result ! (and algorithm fails otherwise) clr %o2 sethi %hi(1 << (32 - 4 - 1)), %g1 cmp %o3, %g1 blu Lnot_really_big clr %o4 ! Here the dividend is >= 2^(31-N) or so. We must be careful here, ! as our usual N-at-a-shot divide step will cause overflow and havoc. ! The number of bits in the result here is N*ITER+SC, where SC <= N. ! Compute ITER in an unorthodox manner: know we need to shift V into ! the top decade: so do not even bother to compare to R. 1: cmp %o5, %g1 bgeu 3f mov 1, %g7 sll %o5, 4, %o5 b 1b inc %o4 ! Now compute %g7. 2: addcc %o5, %o5, %o5 bcc Lnot_too_big inc %g7 ! We get here if the %o1 overflowed while shifting. ! This means that %o3 has the high-order bit set. ! Restore %o5 and subtract from %o3. sll %g1, 4, %g1 ! high order bit srl %o5, 1, %o5 ! rest of %o5 add %o5, %g1, %o5 b Ldo_single_div dec %g7 Lnot_too_big: 3: cmp %o5, %o3 blu 2b nop be Ldo_single_div nop /* NB: these are commented out in the V8-Sparc manual as well */ /* (I do not understand this) */ ! %o5 > %o3: went too far: back up 1 step ! srl %o5, 1, %o5 ! dec %g7 ! do single-bit divide steps ! ! We have to be careful here. We know that %o3 >= %o5, so we can do the ! first divide step without thinking. BUT, the others are conditional, ! and are only done if %o3 >= 0. Because both %o3 and %o5 may have the high- ! order bit set in the first step, just falling into the regular ! division loop will mess up the first time around. ! So we unroll slightly... Ldo_single_div: deccc %g7 bl Lend_regular_divide nop sub %o3, %o5, %o3 mov 1, %o2 b Lend_single_divloop nop Lsingle_divloop: sll %o2, 1, %o2 bl 1f srl %o5, 1, %o5 ! %o3 >= 0 sub %o3, %o5, %o3 b 2f inc %o2 1: ! %o3 < 0 add %o3, %o5, %o3 dec %o2 2: Lend_single_divloop: deccc %g7 bge Lsingle_divloop tst %o3 b,a Lend_regular_divide Lnot_really_big: 1: sll %o5, 4, %o5 cmp %o5, %o3 bleu 1b inccc %o4 be Lgot_result dec %o4 tst %o3 ! set up for initial iteration Ldivloop: sll %o2, 4, %o2 ! depth 1, accumulated bits 0 bl L.1.16 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 2, accumulated bits 1 bl L.2.17 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 3, accumulated bits 3 bl L.3.19 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 4, accumulated bits 7 bl L.4.23 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (7*2+1), %o2 L.4.23: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (7*2-1), %o2 L.3.19: ! remainder is negative addcc %o3,%o5,%o3 ! depth 4, accumulated bits 5 bl L.4.21 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (5*2+1), %o2 L.4.21: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (5*2-1), %o2 L.2.17: ! remainder is negative addcc %o3,%o5,%o3 ! depth 3, accumulated bits 1 bl L.3.17 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 4, accumulated bits 3 bl L.4.19 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (3*2+1), %o2 L.4.19: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (3*2-1), %o2 L.3.17: ! remainder is negative addcc %o3,%o5,%o3 ! depth 4, accumulated bits 1 bl L.4.17 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (1*2+1), %o2 L.4.17: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (1*2-1), %o2 L.1.16: ! remainder is negative addcc %o3,%o5,%o3 ! depth 2, accumulated bits -1 bl L.2.15 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 3, accumulated bits -1 bl L.3.15 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 4, accumulated bits -1 bl L.4.15 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (-1*2+1), %o2 L.4.15: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (-1*2-1), %o2 L.3.15: ! remainder is negative addcc %o3,%o5,%o3 ! depth 4, accumulated bits -3 bl L.4.13 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (-3*2+1), %o2 L.4.13: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (-3*2-1), %o2 L.2.15: ! remainder is negative addcc %o3,%o5,%o3 ! depth 3, accumulated bits -3 bl L.3.13 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 ! depth 4, accumulated bits -5 bl L.4.11 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (-5*2+1), %o2 L.4.11: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (-5*2-1), %o2 L.3.13: ! remainder is negative addcc %o3,%o5,%o3 ! depth 4, accumulated bits -7 bl L.4.9 srl %o5,1,%o5 ! remainder is positive subcc %o3,%o5,%o3 b 9f add %o2, (-7*2+1), %o2 L.4.9: ! remainder is negative addcc %o3,%o5,%o3 b 9f add %o2, (-7*2-1), %o2 9: Lend_regular_divide: deccc %o4 bge Ldivloop tst %o3 bl,a Lgot_result ! non-restoring fixup here (one instruction only!) dec %o2 Lgot_result: ! check to see if answer should be < 0 tst %g6 bl,a 1f neg %o2 1: retl mov %o2, %o0