log2.h

  1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/* Integer base 2 logarithm calculation
  3 *
  4 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
  5 * Written by David Howells (dhowells@redhat.com)
  6 */
  7
  8#ifndef _TOOLS_LINUX_LOG2_H
  9#define _TOOLS_LINUX_LOG2_H
 10
 11#include <linux/bitops.h>
 12#include <linux/types.h>
 13
 14/*
 15 * non-constant log of base 2 calculators
 16 * - the arch may override these in asm/bitops.h if they can be implemented
 17 *   more efficiently than using fls() and fls64()
 18 * - the arch is not required to handle n==0 if implementing the fallback
 19 */
 20static inline __attribute__((const))
 21int __ilog2_u32(u32 n)
 22{
 23	return fls(n) - 1;
 24}
 25
 26static inline __attribute__((const))
 27int __ilog2_u64(u64 n)
 28{
 29	return fls64(n) - 1;
 30}
 31
 32/*
 33 *  Determine whether some value is a power of two, where zero is
 34 * *not* considered a power of two.
 35 */
 36
 37static inline __attribute__((const))
 38bool is_power_of_2(unsigned long n)
 39{
 40	return (n != 0 && ((n & (n - 1)) == 0));
 41}
 42
 43/*
 44 * round up to nearest power of two
 45 */
 46static inline __attribute__((const))
 47unsigned long __roundup_pow_of_two(unsigned long n)
 48{
 49	return 1UL << fls_long(n - 1);
 50}
 51
 52/*
 53 * round down to nearest power of two
 54 */
 55static inline __attribute__((const))
 56unsigned long __rounddown_pow_of_two(unsigned long n)
 57{
 58	return 1UL << (fls_long(n) - 1);
 59}
 60
 61/**
 62 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
 63 * @n - parameter
 64 *
 65 * constant-capable log of base 2 calculation
 66 * - this can be used to initialise global variables from constant data, hence
 67 *   the massive ternary operator construction
 68 *
 69 * selects the appropriately-sized optimised version depending on sizeof(n)
 70 */
 71#define ilog2(n)				\
 72(						\
 73	__builtin_constant_p(n) ? (		\
 74		(n) < 2 ? 0 :			\
 75		(n) & (1ULL << 63) ? 63 :	\
 76		(n) & (1ULL << 62) ? 62 :	\
 77		(n) & (1ULL << 61) ? 61 :	\
 78		(n) & (1ULL << 60) ? 60 :	\
 79		(n) & (1ULL << 59) ? 59 :	\
 80		(n) & (1ULL << 58) ? 58 :	\
 81		(n) & (1ULL << 57) ? 57 :	\
 82		(n) & (1ULL << 56) ? 56 :	\
 83		(n) & (1ULL << 55) ? 55 :	\
 84		(n) & (1ULL << 54) ? 54 :	\
 85		(n) & (1ULL << 53) ? 53 :	\
 86		(n) & (1ULL << 52) ? 52 :	\
 87		(n) & (1ULL << 51) ? 51 :	\
 88		(n) & (1ULL << 50) ? 50 :	\
 89		(n) & (1ULL << 49) ? 49 :	\
 90		(n) & (1ULL << 48) ? 48 :	\
 91		(n) & (1ULL << 47) ? 47 :	\
 92		(n) & (1ULL << 46) ? 46 :	\
 93		(n) & (1ULL << 45) ? 45 :	\
 94		(n) & (1ULL << 44) ? 44 :	\
 95		(n) & (1ULL << 43) ? 43 :	\
 96		(n) & (1ULL << 42) ? 42 :	\
 97		(n) & (1ULL << 41) ? 41 :	\
 98		(n) & (1ULL << 40) ? 40 :	\
 99		(n) & (1ULL << 39) ? 39 :	\
100		(n) & (1ULL << 38) ? 38 :	\
101		(n) & (1ULL << 37) ? 37 :	\
102		(n) & (1ULL << 36) ? 36 :	\
103		(n) & (1ULL << 35) ? 35 :	\
104		(n) & (1ULL << 34) ? 34 :	\
105		(n) & (1ULL << 33) ? 33 :	\
106		(n) & (1ULL << 32) ? 32 :	\
107		(n) & (1ULL << 31) ? 31 :	\
108		(n) & (1ULL << 30) ? 30 :	\
109		(n) & (1ULL << 29) ? 29 :	\
110		(n) & (1ULL << 28) ? 28 :	\
111		(n) & (1ULL << 27) ? 27 :	\
112		(n) & (1ULL << 26) ? 26 :	\
113		(n) & (1ULL << 25) ? 25 :	\
114		(n) & (1ULL << 24) ? 24 :	\
115		(n) & (1ULL << 23) ? 23 :	\
116		(n) & (1ULL << 22) ? 22 :	\
117		(n) & (1ULL << 21) ? 21 :	\
118		(n) & (1ULL << 20) ? 20 :	\
119		(n) & (1ULL << 19) ? 19 :	\
120		(n) & (1ULL << 18) ? 18 :	\
121		(n) & (1ULL << 17) ? 17 :	\
122		(n) & (1ULL << 16) ? 16 :	\
123		(n) & (1ULL << 15) ? 15 :	\
124		(n) & (1ULL << 14) ? 14 :	\
125		(n) & (1ULL << 13) ? 13 :	\
126		(n) & (1ULL << 12) ? 12 :	\
127		(n) & (1ULL << 11) ? 11 :	\
128		(n) & (1ULL << 10) ? 10 :	\
129		(n) & (1ULL <<  9) ?  9 :	\
130		(n) & (1ULL <<  8) ?  8 :	\
131		(n) & (1ULL <<  7) ?  7 :	\
132		(n) & (1ULL <<  6) ?  6 :	\
133		(n) & (1ULL <<  5) ?  5 :	\
134		(n) & (1ULL <<  4) ?  4 :	\
135		(n) & (1ULL <<  3) ?  3 :	\
136		(n) & (1ULL <<  2) ?  2 :	\
137		1 ) :				\
138	(sizeof(n) <= 4) ?			\
139	__ilog2_u32(n) :			\
140	__ilog2_u64(n)				\
141 )
142
143/**
144 * roundup_pow_of_two - round the given value up to nearest power of two
145 * @n - parameter
146 *
147 * round the given value up to the nearest power of two
148 * - the result is undefined when n == 0
149 * - this can be used to initialise global variables from constant data
150 */
151#define roundup_pow_of_two(n)			\
152(						\
153	__builtin_constant_p(n) ? (		\
154		(n == 1) ? 1 :			\
155		(1UL << (ilog2((n) - 1) + 1))	\
156				   ) :		\
157	__roundup_pow_of_two(n)			\
158 )
159
160/**
161 * rounddown_pow_of_two - round the given value down to nearest power of two
162 * @n - parameter
163 *
164 * round the given value down to the nearest power of two
165 * - the result is undefined when n == 0
166 * - this can be used to initialise global variables from constant data
167 */
168#define rounddown_pow_of_two(n)			\
169(						\
170	__builtin_constant_p(n) ? (		\
171		(1UL << ilog2(n))) :		\
172	__rounddown_pow_of_two(n)		\
173 )
174
175#endif /* _TOOLS_LINUX_LOG2_H */