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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>
40 lines
691 B
C
40 lines
691 B
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
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*
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* Based on the shift-and-subtract algorithm for computing integer
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* square root from Guy L. Steele.
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*/
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#include <linux/kernel.h>
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#include <linux/export.h>
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#include <linux/bitops.h>
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/**
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* int_sqrt - computes the integer square root
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* @x: integer of which to calculate the sqrt
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*
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* Computes: floor(sqrt(x))
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*/
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unsigned long int_sqrt(unsigned long x)
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{
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unsigned long b, m, y = 0;
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if (x <= 1)
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return x;
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m = 1UL << (__fls(x) & ~1UL);
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while (m != 0) {
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b = y + m;
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y >>= 1;
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if (x >= b) {
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x -= b;
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y += m;
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}
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m >>= 2;
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}
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return y;
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}
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EXPORT_SYMBOL(int_sqrt);
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