mirror of
https://github.com/torvalds/linux.git
synced 2024-11-05 03:21:32 +00:00
658716d19f
The current implementation of div64_u64 for 32bit systems returns an approximately correct result when the divisor exceeds 32bits. Since doing 64bit division using 32bit hardware is a long since solved problem we just use one of the existing proven methods. Additionally, add a div64_s64 function to correctly handle doing signed 64bit division. Addresses https://bugzilla.redhat.com/show_bug.cgi?id=616105 Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Ben Woodard <bwoodard@llnl.gov> Cc: Jeremy Fitzhardinge <jeremy@goop.org> Cc: Mark Grondona <mgrondona@llnl.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
143 lines
3.1 KiB
C
143 lines
3.1 KiB
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/module.h>
|
|
#include <linux/math64.h>
|
|
|
|
/* Not needed on 64bit architectures */
|
|
#if BITS_PER_LONG == 32
|
|
|
|
uint32_t __attribute__((weak)) __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);
|
|
|
|
#ifndef div_s64_rem
|
|
s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
|
|
{
|
|
u64 quotient;
|
|
|
|
if (dividend < 0) {
|
|
quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
|
|
*remainder = -*remainder;
|
|
if (divisor > 0)
|
|
quotient = -quotient;
|
|
} else {
|
|
quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
|
|
if (divisor < 0)
|
|
quotient = -quotient;
|
|
}
|
|
return quotient;
|
|
}
|
|
EXPORT_SYMBOL(div_s64_rem);
|
|
#endif
|
|
|
|
/**
|
|
* div64_u64 - unsigned 64bit divide with 64bit divisor
|
|
* @dividend: 64bit dividend
|
|
* @divisor: 64bit divisor
|
|
*
|
|
* This implementation is a modified version of the algorithm proposed
|
|
* by the book 'Hacker's Delight'. The original source and full proof
|
|
* can be found here and is available for use without restriction.
|
|
*
|
|
* 'http://www.hackersdelight.org/HDcode/newCode/divDouble.c'
|
|
*/
|
|
#ifndef div64_u64
|
|
u64 div64_u64(u64 dividend, u64 divisor)
|
|
{
|
|
u32 high = divisor >> 32;
|
|
u64 quot;
|
|
|
|
if (high == 0) {
|
|
quot = div_u64(dividend, divisor);
|
|
} else {
|
|
int n = 1 + fls(high);
|
|
quot = div_u64(dividend >> n, divisor >> n);
|
|
|
|
if (quot != 0)
|
|
quot--;
|
|
if ((dividend - quot * divisor) >= divisor)
|
|
quot++;
|
|
}
|
|
|
|
return quot;
|
|
}
|
|
EXPORT_SYMBOL(div64_u64);
|
|
#endif
|
|
|
|
/**
|
|
* div64_s64 - signed 64bit divide with 64bit divisor
|
|
* @dividend: 64bit dividend
|
|
* @divisor: 64bit divisor
|
|
*/
|
|
#ifndef div64_s64
|
|
s64 div64_s64(s64 dividend, s64 divisor)
|
|
{
|
|
s64 quot, t;
|
|
|
|
quot = div64_u64(abs64(dividend), abs64(divisor));
|
|
t = (dividend ^ divisor) >> 63;
|
|
|
|
return (quot ^ t) - t;
|
|
}
|
|
EXPORT_SYMBOL(div64_s64);
|
|
#endif
|
|
|
|
#endif /* BITS_PER_LONG == 32 */
|
|
|
|
/*
|
|
* Iterative div/mod for use when dividend is not expected to be much
|
|
* bigger than divisor.
|
|
*/
|
|
u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
|
|
{
|
|
return __iter_div_u64_rem(dividend, divisor, remainder);
|
|
}
|
|
EXPORT_SYMBOL(iter_div_u64_rem);
|