root/lib/div64.c

/*
 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
 *
 * Based on former do_div() implementation from asm-parisc/div64.h:
 *      Copyright (C) 1999 Hewlett-Packard Co
 *      Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
 *
 *
 * Generic C version of 64bit/32bit division and modulo, with
 * 64bit result and 32bit remainder.
 *
 * The fast case for (n>>32 == 0) is handled inline by do_div(). 
 *
 * Code generated for this function might be very inefficient
 * for some CPUs. __div64_32() can be overridden by linking arch-specific
 * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
 */

#include <linux/types.h>
#include <linux/module.h>
#include <asm/div64.h>

/* Not needed on 64bit architectures */
#if BITS_PER_LONG == 32

uint32_t __div64_32(uint64_t *n, uint32_t base)
{
        uint64_t rem = *n;
        uint64_t b = base;
        uint64_t res, d = 1;
        uint32_t high = rem >> 32;

        /* Reduce the thing a bit first */
        res = 0;
        if (high >= base) {
                high /= base;
                res = (uint64_t) high << 32;
                rem -= (uint64_t) (high*base) << 32;
        }

        while ((int64_t)b > 0 && b < rem) {
                b = b+b;
                d = d+d;
        }

        do {
                if (rem >= b) {
                        rem -= b;
                        res += d;
                }
                b >>= 1;
                d >>= 1;
        } while (d);

        *n = res;
        return rem;
}

EXPORT_SYMBOL(__div64_32);

#endif /* BITS_PER_LONG == 32 */