linux-stable/lib/int_sqrt.c
Crt Mori 47a3616348 lib: Add strongly typed 64bit int_sqrt
There is no option to perform 64bit integer sqrt on 32bit platform.
Added stronger typed int_sqrt64 enables the 64bit calculations to
be performed on 32bit platforms. Using same algorithm as int_sqrt()
with strong typing provides enough precision also on 32bit platforms,
but it sacrifices some performance. In case values are smaller than
ULONG_MAX the standard int_sqrt is used for calculation to maximize the
performance due to more native calculations.

Signed-off-by: Crt Mori <cmo@melexis.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
2018-02-04 10:17:21 +00:00

70 lines
1.1 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
*
* Based on the shift-and-subtract algorithm for computing integer
* square root from Guy L. Steele.
*/
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/bitops.h>
/**
* int_sqrt - computes the integer square root
* @x: integer of which to calculate the sqrt
*
* Computes: floor(sqrt(x))
*/
unsigned long int_sqrt(unsigned long x)
{
unsigned long b, m, y = 0;
if (x <= 1)
return x;
m = 1UL << (__fls(x) & ~1UL);
while (m != 0) {
b = y + m;
y >>= 1;
if (x >= b) {
x -= b;
y += m;
}
m >>= 2;
}
return y;
}
EXPORT_SYMBOL(int_sqrt);
#if BITS_PER_LONG < 64
/**
* int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
* is expected.
* @x: 64bit integer of which to calculate the sqrt
*/
u32 int_sqrt64(u64 x)
{
u64 b, m, y = 0;
if (x <= ULONG_MAX)
return int_sqrt((unsigned long) x);
m = 1ULL << (fls64(x) & ~1ULL);
while (m != 0) {
b = y + m;
y >>= 1;
if (x >= b) {
x -= b;
y += m;
}
m >>= 2;
}
return y;
}
EXPORT_SYMBOL(int_sqrt64);
#endif