254 lines
11 KiB
C
254 lines
11 KiB
C
/* Integer base 2 logarithm calculation
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*
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* Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#ifndef _LINUX_LOG2_H
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#define _LINUX_LOG2_H
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#include <linux/fls.h>
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#include <linux/fls64.h>
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#include <linux/types.h>
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#include <linux/bitops.h>
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/*
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* non-constant log of base 2 calculators
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* - the arch may override these in asm/bitops.h if they can be implemented
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* more efficiently than using fls() and fls64()
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* - the arch is not required to handle n==0 if implementing the fallback
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*/
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#ifndef CONFIG_ARCH_HAS_ILOG2_U32
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static inline __attribute__((const)) int __ilog2_u32(u32 n)
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{
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return fls(n) - 1;
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}
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#endif
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#ifndef CONFIG_ARCH_HAS_ILOG2_U64
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static inline __attribute__((const)) int __ilog2_u64(u64 n)
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{
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return fls64(n) - 1;
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}
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#endif
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/*
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* Determine whether some value is a power of two, where zero is
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* *not* considered a power of two.
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*/
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static inline __attribute__((const)) bool is_power_of_2(unsigned long n)
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{
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return (n != 0 && ((n & (n - 1)) == 0));
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}
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/*
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* round up to nearest power of two
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*/
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static inline __attribute__((const)) unsigned long
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__roundup_pow_of_two(unsigned long n)
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{
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return 1UL << fls_long(n - 1);
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}
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/*
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* round down to nearest power of two
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*/
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static inline __attribute__((const)) unsigned long
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__rounddown_pow_of_two(unsigned long n)
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{
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return 1UL << (fls_long(n) - 1);
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}
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/**
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* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
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* @n - parameter
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*
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* constant-capable log of base 2 calculation
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* - this can be used to initialise global variables from constant data, hence
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* the massive ternary operator construction
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*
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* selects the appropriately-sized optimised version depending on sizeof(n)
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*/
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#define ilog2(n) \
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(__builtin_constant_p(n) ? \
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((n) < 2 ? 0 : \
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(n) & (1ULL << 63) ? \
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63 : \
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(n) & (1ULL << 62) ? \
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62 : \
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(n) & (1ULL << 61) ? \
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61 : \
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(n) & (1ULL << 60) ? \
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60 : \
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(n) & (1ULL << 59) ? \
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59 : \
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(n) & (1ULL << 58) ? \
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58 : \
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(n) & (1ULL << 57) ? \
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57 : \
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(n) & (1ULL << 56) ? \
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56 : \
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(n) & (1ULL << 55) ? \
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55 : \
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(n) & (1ULL << 54) ? \
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54 : \
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(n) & (1ULL << 53) ? \
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53 : \
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(n) & (1ULL << 52) ? \
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52 : \
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(n) & (1ULL << 51) ? \
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51 : \
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(n) & (1ULL << 50) ? \
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50 : \
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(n) & (1ULL << 49) ? \
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49 : \
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(n) & (1ULL << 48) ? \
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48 : \
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(n) & (1ULL << 47) ? \
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47 : \
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(n) & (1ULL << 46) ? \
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46 : \
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(n) & (1ULL << 45) ? \
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45 : \
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(n) & (1ULL << 44) ? \
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44 : \
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(n) & (1ULL << 43) ? \
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43 : \
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(n) & (1ULL << 42) ? \
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42 : \
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(n) & (1ULL << 41) ? \
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41 : \
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(n) & (1ULL << 40) ? \
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40 : \
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(n) & (1ULL << 39) ? \
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39 : \
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(n) & (1ULL << 38) ? \
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38 : \
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(n) & (1ULL << 37) ? \
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37 : \
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(n) & (1ULL << 36) ? \
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36 : \
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(n) & (1ULL << 35) ? \
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35 : \
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(n) & (1ULL << 34) ? \
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34 : \
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(n) & (1ULL << 33) ? \
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33 : \
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(n) & (1ULL << 32) ? \
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32 : \
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(n) & (1ULL << 31) ? \
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31 : \
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(n) & (1ULL << 30) ? \
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30 : \
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(n) & (1ULL << 29) ? \
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29 : \
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(n) & (1ULL << 28) ? \
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28 : \
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(n) & (1ULL << 27) ? \
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27 : \
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(n) & (1ULL << 26) ? \
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26 : \
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(n) & (1ULL << 25) ? \
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25 : \
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(n) & (1ULL << 24) ? \
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24 : \
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(n) & (1ULL << 23) ? \
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23 : \
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(n) & (1ULL << 22) ? \
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22 : \
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(n) & (1ULL << 21) ? \
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21 : \
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(n) & (1ULL << 20) ? \
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20 : \
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(n) & (1ULL << 19) ? \
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19 : \
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(n) & (1ULL << 18) ? \
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18 : \
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(n) & (1ULL << 17) ? \
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17 : \
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(n) & (1ULL << 16) ? \
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16 : \
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(n) & (1ULL << 15) ? \
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15 : \
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(n) & (1ULL << 14) ? \
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14 : \
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(n) & (1ULL << 13) ? \
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13 : \
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(n) & (1ULL << 12) ? \
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12 : \
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(n) & (1ULL << 11) ? \
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11 : \
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(n) & (1ULL << 10) ? \
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10 : \
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(n) & (1ULL << 9) ? \
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9 : \
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(n) & (1ULL << 8) ? \
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8 : \
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(n) & (1ULL << 7) ? \
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7 : \
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(n) & (1ULL << 6) ? \
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6 : \
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(n) & (1ULL << 5) ? \
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5 : \
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(n) & (1ULL << 4) ? \
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4 : \
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(n) & (1ULL << 3) ? 3 : \
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(n) & (1ULL << 2) ? 2 : 1) : \
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(sizeof(n) <= 4) ? __ilog2_u32(n) : __ilog2_u64(n))
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/**
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* roundup_pow_of_two - round the given value up to nearest power of two
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* @n - parameter
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*
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* round the given value up to the nearest power of two
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* - the result is undefined when n == 0
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* - this can be used to initialise global variables from constant data
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*/
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#define roundup_pow_of_two(n) \
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(__builtin_constant_p(n) ? \
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((n == 1) ? 1 : (1UL << (ilog2((n)-1) + 1))) : \
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__roundup_pow_of_two(n))
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/**
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* rounddown_pow_of_two - round the given value down to nearest power of two
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* @n - parameter
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*
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* round the given value down to the nearest power of two
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* - the result is undefined when n == 0
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* - this can be used to initialise global variables from constant data
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*/
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#define rounddown_pow_of_two(n) \
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(__builtin_constant_p(n) ? ((1UL << ilog2(n))) : \
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__rounddown_pow_of_two(n))
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/**
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* order_base_2 - calculate the (rounded up) base 2 order of the argument
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* @n: parameter
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*
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* The first few values calculated by this routine:
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* ob2(0) = 0
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* ob2(1) = 0
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* ob2(2) = 1
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* ob2(3) = 2
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* ob2(4) = 2
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* ob2(5) = 3
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* ... and so on.
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*/
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static inline __attribute_const__ int __order_base_2(unsigned long n)
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{
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return n > 1 ? ilog2(n - 1) + 1 : 0;
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}
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#define order_base_2(n) \
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(__builtin_constant_p(n) ? \
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(((n) == 0 || (n) == 1) ? 0 : ilog2((n)-1) + 1) : \
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__order_base_2(n))
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#endif /* _LINUX_LOG2_H */
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