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29905b52fa
The function order_base_2() is defined (according to the comment block)
as returning zero on input zero, but subsequently passes the input into
roundup_pow_of_two(), which is explicitly undefined for input zero.
This has gone unnoticed until now, but optimization passes in GCC 7 may
produce constant folded function instances where a constant value of
zero is passed into order_base_2(), resulting in link errors against the
deliberately undefined '____ilog2_NaN'.
So update order_base_2() to adhere to its own documented interface.
[ See
http://marc.info/?l=linux-kernel&m=147672952517795&w=2
and follow-up discussion for more background. The gcc "optimization
pass" is really just broken, but now the GCC trunk problem seems to
have escaped out of just specially built daily images, so we need to
work around it in mainline. - Linus ]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
219 lines
5.5 KiB
C
219 lines
5.5 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/types.h>
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#include <linux/bitops.h>
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/*
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* deal with unrepresentable constant logarithms
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*/
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extern __attribute__((const, noreturn))
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int ____ilog2_NaN(void);
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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))
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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))
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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))
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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))
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unsigned long __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))
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unsigned long __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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( \
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__builtin_constant_p(n) ? ( \
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(n) < 1 ? ____ilog2_NaN() : \
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(n) & (1ULL << 63) ? 63 : \
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(n) & (1ULL << 62) ? 62 : \
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(n) & (1ULL << 61) ? 61 : \
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(n) & (1ULL << 60) ? 60 : \
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(n) & (1ULL << 59) ? 59 : \
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(n) & (1ULL << 58) ? 58 : \
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(n) & (1ULL << 57) ? 57 : \
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(n) & (1ULL << 56) ? 56 : \
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(n) & (1ULL << 55) ? 55 : \
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(n) & (1ULL << 54) ? 54 : \
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(n) & (1ULL << 53) ? 53 : \
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(n) & (1ULL << 52) ? 52 : \
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(n) & (1ULL << 51) ? 51 : \
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(n) & (1ULL << 50) ? 50 : \
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(n) & (1ULL << 49) ? 49 : \
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(n) & (1ULL << 48) ? 48 : \
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(n) & (1ULL << 47) ? 47 : \
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(n) & (1ULL << 46) ? 46 : \
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(n) & (1ULL << 45) ? 45 : \
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(n) & (1ULL << 44) ? 44 : \
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(n) & (1ULL << 43) ? 43 : \
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(n) & (1ULL << 42) ? 42 : \
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(n) & (1ULL << 41) ? 41 : \
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(n) & (1ULL << 40) ? 40 : \
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(n) & (1ULL << 39) ? 39 : \
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(n) & (1ULL << 38) ? 38 : \
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(n) & (1ULL << 37) ? 37 : \
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(n) & (1ULL << 36) ? 36 : \
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(n) & (1ULL << 35) ? 35 : \
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(n) & (1ULL << 34) ? 34 : \
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(n) & (1ULL << 33) ? 33 : \
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(n) & (1ULL << 32) ? 32 : \
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(n) & (1ULL << 31) ? 31 : \
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(n) & (1ULL << 30) ? 30 : \
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(n) & (1ULL << 29) ? 29 : \
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(n) & (1ULL << 28) ? 28 : \
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(n) & (1ULL << 27) ? 27 : \
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(n) & (1ULL << 26) ? 26 : \
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(n) & (1ULL << 25) ? 25 : \
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(n) & (1ULL << 24) ? 24 : \
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(n) & (1ULL << 23) ? 23 : \
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(n) & (1ULL << 22) ? 22 : \
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(n) & (1ULL << 21) ? 21 : \
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(n) & (1ULL << 20) ? 20 : \
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(n) & (1ULL << 19) ? 19 : \
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(n) & (1ULL << 18) ? 18 : \
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(n) & (1ULL << 17) ? 17 : \
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(n) & (1ULL << 16) ? 16 : \
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(n) & (1ULL << 15) ? 15 : \
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(n) & (1ULL << 14) ? 14 : \
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(n) & (1ULL << 13) ? 13 : \
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(n) & (1ULL << 12) ? 12 : \
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(n) & (1ULL << 11) ? 11 : \
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(n) & (1ULL << 10) ? 10 : \
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(n) & (1ULL << 9) ? 9 : \
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(n) & (1ULL << 8) ? 8 : \
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(n) & (1ULL << 7) ? 7 : \
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(n) & (1ULL << 6) ? 6 : \
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(n) & (1ULL << 5) ? 5 : \
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(n) & (1ULL << 4) ? 4 : \
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(n) & (1ULL << 3) ? 3 : \
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(n) & (1ULL << 2) ? 2 : \
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(n) & (1ULL << 1) ? 1 : \
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(n) & (1ULL << 0) ? 0 : \
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____ilog2_NaN() \
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) : \
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(sizeof(n) <= 4) ? \
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__ilog2_u32(n) : \
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__ilog2_u64(n) \
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)
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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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( \
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__builtin_constant_p(n) ? ( \
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(n == 1) ? 1 : \
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(1UL << (ilog2((n) - 1) + 1)) \
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) : \
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__roundup_pow_of_two(n) \
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)
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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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( \
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__builtin_constant_p(n) ? ( \
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(1UL << ilog2(n))) : \
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__rounddown_pow_of_two(n) \
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)
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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__
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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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( \
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__builtin_constant_p(n) ? ( \
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((n) == 0 || (n) == 1) ? 0 : \
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ilog2((n) - 1) + 1) : \
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__order_base_2(n) \
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)
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#endif /* _LINUX_LOG2_H */
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