mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-06 03:16:39 +07:00
cdc94a3749
fls counts bits starting from 1 to 32 (returns 0 for zero argument). If
we add 1 we shift right one bit more and loose precision from divisor,
what cause function incorect results with some numbers.
Corrected code was tested in user-space, see bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=202391
Link: http://lkml.kernel.org/r/1548686944-11891-1-git-send-email-sgruszka@redhat.com
Fixes: 658716d19f
("div64_u64(): improve precision on 32bit platforms")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reported-by: Siarhei Volkau <lis8215@gmail.com>
Tested-by: Siarhei Volkau <lis8215@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
193 lines
4.2 KiB
C
193 lines
4.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* 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
|
|
* or by defining a preprocessor macro in arch/include/asm/div64.h.
|
|
*/
|
|
|
|
#include <linux/export.h>
|
|
#include <linux/kernel.h>
|
|
#include <linux/math64.h>
|
|
|
|
/* Not needed on 64bit architectures */
|
|
#if BITS_PER_LONG == 32
|
|
|
|
#ifndef __div64_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);
|
|
#endif
|
|
|
|
/**
|
|
* div_s64_rem - signed 64bit divide with 64bit divisor and remainder
|
|
* @dividend: 64bit dividend
|
|
* @divisor: 64bit divisor
|
|
* @remainder: 64bit remainder
|
|
*/
|
|
#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_rem - unsigned 64bit divide with 64bit divisor and remainder
|
|
* @dividend: 64bit dividend
|
|
* @divisor: 64bit divisor
|
|
* @remainder: 64bit remainder
|
|
*
|
|
* This implementation is a comparable to algorithm used by div64_u64.
|
|
* But this operation, which includes math for calculating the remainder,
|
|
* is kept distinct to avoid slowing down the div64_u64 operation on 32bit
|
|
* systems.
|
|
*/
|
|
#ifndef div64_u64_rem
|
|
u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
|
|
{
|
|
u32 high = divisor >> 32;
|
|
u64 quot;
|
|
|
|
if (high == 0) {
|
|
u32 rem32;
|
|
quot = div_u64_rem(dividend, divisor, &rem32);
|
|
*remainder = rem32;
|
|
} else {
|
|
int n = fls(high);
|
|
quot = div_u64(dividend >> n, divisor >> n);
|
|
|
|
if (quot != 0)
|
|
quot--;
|
|
|
|
*remainder = dividend - quot * divisor;
|
|
if (*remainder >= divisor) {
|
|
quot++;
|
|
*remainder -= divisor;
|
|
}
|
|
}
|
|
|
|
return quot;
|
|
}
|
|
EXPORT_SYMBOL(div64_u64_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/hdcodetxt/divDouble.c.txt'
|
|
*/
|
|
#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 = 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(abs(dividend), abs(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);
|