LXR linux/lib/math/int

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
   4 *
   5 *  Based on the shift-and-subtract algorithm for computing integer
   6 *  square root from Guy L. Steele.
   7 */
   8
   9#include <linux/export.h>
  10#include <linux/bitops.h>
  11#include <linux/limits.h>
  12#include <linux/math.h>
  13
  14/**
  15 * int_sqrt - computes the integer square root
  16 * @x: integer of which to calculate the sqrt
  17 *
  18 * Computes: floor(sqrt(x))
  19 */
  20unsigned long int_sqrt(unsigned long x)
  21{
  22        unsigned long b, m, y = 0;
  23
  24        if (x <= 1)
  25                return x;
  26
  27        m = 1UL << (__fls(x) & ~1UL);
  28        while (m != 0) {
  29                b = y + m;
  30                y >>= 1;
  31
  32                if (x >= b) {
  33                        x -= b;
  34                        y += m;
  35                }
  36                m >>= 2;
  37        }
  38
  39        return y;
  40}
  41EXPORT_SYMBOL(int_sqrt);
  42
  43#if BITS_PER_LONG < 64
  44/**
  45 * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
  46 * is expected.
  47 * @x: 64bit integer of which to calculate the sqrt
  48 */
  49u32 int_sqrt64(u64 x)
  50{
  51        u64 b, m, y = 0;
  52
  53        if (x <= ULONG_MAX)
  54                return int_sqrt((unsigned long) x);
  55
  56        m = 1ULL << ((fls64(x) - 1) & ~1ULL);
  57        while (m != 0) {
  58                b = y + m;
  59                y >>= 1;
  60
  61                if (x >= b) {
  62                        x -= b;
  63                        y += m;
  64                }
  65                m >>= 2;
  66        }
  67
  68        return y;
  69}
  70EXPORT_SYMBOL(int_sqrt64);
  71#endif
  72