e813a61400
Our current int_sqrt() is not rough nor any approximation; it calculates the exact value of: floor(sqrt()). Document this. Link: http://lkml.kernel.org/r/20171020164645.001652117@infradead.org Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Anshul Garg <aksgarg1989@gmail.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: David Miller <davem@davemloft.net> Cc: Ingo Molnar <mingo@kernel.org> Cc: Joe Perches <joe@perches.com> Cc: Kees Cook <keescook@chromium.org> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: Michael Davidson <md@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
41 lines
691 B
C
41 lines
691 B
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);
|