source: mainline/uspace/lib/softint/generic/division.c@ 88d5c1e

/*
 * Copyright (c) 2006 Josef Cejka
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - 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.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
 */

/** @addtogroup softint
 * @{
 */ 
/**
 * @file
 * SW implementation of 32 and 64 bit division and modulo.
 */

#include <division.h>

#define ABSVAL(x)  ((x) > 0 ? (x) : -(x))
#define SGN(x)     ((x) >= 0 ? 1 : 0)

static unsigned int divandmod32(unsigned int a, unsigned int b,
    unsigned int *remainder)
{
        unsigned int result;
        int steps = sizeof(unsigned int) * 8; 
        
        *remainder = 0;
        result = 0;
        
        if (b == 0) {
                /* FIXME: division by zero */
                return 0;
        }
        
        if (a < b) {
                *remainder = a;
                return 0;
        }
        
        for (; steps > 0; steps--) {
                /* shift one bit to remainder */
                *remainder = ((*remainder) << 1) | (( a >> 31) & 0x1);
                result <<= 1;
                
                if (*remainder >= b) {
                        *remainder -= b;
                        result |= 0x1;
                }
                a <<= 1;
        }
        
        return result;
}

static unsigned long long divandmod64(unsigned long long a,
    unsigned long long b, unsigned long long *remainder)
{
        unsigned long long result;
        int steps = sizeof(unsigned long long) * 8;
        
        *remainder = 0;
        result = 0;
        
        if (b == 0) {
                /* FIXME: division by zero */
                return 0;
        }
        
        if (a < b) {
                *remainder = a;
                return 0;
        }
        
        for (; steps > 0; steps--) {
                /* shift one bit to remainder */
                *remainder = ((*remainder) << 1) | ((a >> 63) & 0x1);
                result <<= 1;
                
                if (*remainder >= b) {
                        *remainder -= b;
                        result |= 0x1;
                }
                a <<= 1;
        }
        
        return result;
}

/* 32bit integer division */
int __divsi3(int a, int b)
{
        unsigned int rem;
        int result = (int) divandmod32(ABSVAL(a), ABSVAL(b), &rem);
        
        if (SGN(a) == SGN(b))
                return result;
        
        return -result;
}

/* 64bit integer division */
long long __divdi3(long long a, long long b)
{
        unsigned long long rem;
        long long result = (long long) divandmod64(ABSVAL(a), ABSVAL(b), &rem);
        
        if (SGN(a) == SGN(b))
                return result;
        
        return -result;
}

/* 32bit unsigned integer division */
unsigned int __udivsi3(unsigned int a, unsigned int b)
{
        unsigned int rem;
        return divandmod32(a, b, &rem);
}

/* 64bit unsigned integer division */
unsigned long long __udivdi3(unsigned long long a, unsigned long long b)
{
        unsigned long long rem;
        return divandmod64(a, b, &rem);
}

/* 32bit remainder of the signed division */
int __modsi3(int a, int b)
{
        unsigned int rem;
        divandmod32(a, b, &rem);
        
        /* if divident is negative, remainder must be too */
        if (!(SGN(a)))
                return -((int) rem);
        
        return (int) rem;
}

/* 64bit remainder of the signed division */
long long __moddi3(long long a, long long b)
{
        unsigned long long rem;
        divandmod64(a, b, &rem);
        
        /* if divident is negative, remainder must be too */
        if (!(SGN(a)))
                return -((long long) rem);
        
        return (long long) rem;
}

/* 32bit remainder of the unsigned division */
unsigned int __umodsi3(unsigned int a, unsigned int b)
{
        unsigned int rem;
        divandmod32(a, b, &rem);
        return rem;
}

/* 64bit remainder of the unsigned division */
unsigned long long __umoddi3(unsigned long long a, unsigned long long b)
{
        unsigned long long rem;
        divandmod64(a, b, &rem);
        return rem;
}

int __divmodsi3(int a, int b, int *c)
{
        unsigned int rem;
        int result = (int) divandmod32(ABSVAL(a), ABSVAL(b), &rem);
        
        if (SGN(a) == SGN(b)) {
                *c = rem;
                return result;
        }
        
        *c = -rem;
        return -result;
}

unsigned int __udivmodsi3(unsigned int a, unsigned int b,
    unsigned int *c)
{
        return divandmod32(a, b, c);
}

long long __divmoddi3(long long a, long long b, long long *c)
{
        unsigned long long rem;
        long long result = (int) divandmod64(ABSVAL(a), ABSVAL(b), &rem);
        
        if (SGN(a) == SGN(b)) {
                *c = rem;
                return result;
        }
        
        *c = -rem;
        return -result;
}

unsigned long long __udivmoddi3(unsigned long long a, unsigned long long b,
    unsigned long long *c)
{
        return divandmod64(a, b, c);
}

/** @}
 */