/* SPDX-License-Identifier: GPL-2.0-or-later */ /* Integer base 2 logarithm calculation * * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. * Written by David Howells (dhowells@redhat.com)
*/
/* * non-constant log of base 2 calculators * - the arch may override these in asm/bitops.h if they can be implemented * more efficiently than using fls() and fls64() * - the arch is not required to handle n==0 if implementing the fallback
*/ #ifndef CONFIG_ARCH_HAS_ILOG2_U32 static __always_inline __attribute__((const)) int __ilog2_u32(u32 n)
{ return fls(n) - 1;
} #endif
/** * is_power_of_2() - check if a value is a power of two * @n: the value to check * * Determine whether some value is a power of two, where zero is * *not* considered a power of two. * Return: true if @n is a power of 2, otherwise false.
*/ static __always_inline __attribute__((const)) bool is_power_of_2(unsignedlong n)
{ return (n != 0 && ((n & (n - 1)) == 0));
}
/** * __roundup_pow_of_two() - round up to nearest power of two * @n: value to round up
*/ staticinline __attribute__((const)) unsignedlong __roundup_pow_of_two(unsignedlong n)
{ return 1UL << fls_long(n - 1);
}
/** * __rounddown_pow_of_two() - round down to nearest power of two * @n: value to round down
*/ staticinline __attribute__((const)) unsignedlong __rounddown_pow_of_two(unsignedlong n)
{ return 1UL << (fls_long(n) - 1);
}
/** * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value * @n: parameter * * constant-capable log of base 2 calculation * - this can be used to initialise global variables from constant data, hence * the massive ternary operator construction * * selects the appropriately-sized optimised version depending on sizeof(n)
*/ #define ilog2(n) \
( \
__builtin_constant_p(n) ? \
((n) < 2 ? 0 : \
63 - __builtin_clzll(n)) : \
(sizeof(n) <= 4) ? \
__ilog2_u32(n) : \
__ilog2_u64(n) \
)
/** * roundup_pow_of_two - round the given value up to nearest power of two * @n: parameter * * round the given value up to the nearest power of two * - the result is undefined when n == 0 * - this can be used to initialise global variables from constant data
*/ #define roundup_pow_of_two(n) \
( \
__builtin_constant_p(n) ? ( \
((n) == 1) ? 1 : \
(1UL << (ilog2((n) - 1) + 1)) \
) : \
__roundup_pow_of_two(n) \
)
/** * rounddown_pow_of_two - round the given value down to nearest power of two * @n: parameter * * round the given value down to the nearest power of two * - the result is undefined when n == 0 * - this can be used to initialise global variables from constant data
*/ #define rounddown_pow_of_two(n) \
( \
__builtin_constant_p(n) ? ( \
(1UL << ilog2(n))) : \
__rounddown_pow_of_two(n) \
)
staticinline __attribute_const__ int __order_base_2(unsignedlong n)
{ return n > 1 ? ilog2(n - 1) + 1 : 0;
}
/** * order_base_2 - calculate the (rounded up) base 2 order of the argument * @n: parameter * * The first few values calculated by this routine: * ob2(0) = 0 * ob2(1) = 0 * ob2(2) = 1 * ob2(3) = 2 * ob2(4) = 2 * ob2(5) = 3 * ... and so on.
*/ #define order_base_2(n) \
( \
__builtin_constant_p(n) ? ( \
((n) == 0 || (n) == 1) ? 0 : \
ilog2((n) - 1) + 1) : \
__order_base_2(n) \
)
staticinline __attribute__((const)) int __bits_per(unsignedlong n)
{ if (n < 2) return 1; if (is_power_of_2(n)) return order_base_2(n) + 1; return order_base_2(n);
}
/** * bits_per - calculate the number of bits required for the argument * @n: parameter * * This is constant-capable and can be used for compile time * initializations, e.g bitfields. * * The first few values calculated by this routine: * bf(0) = 1 * bf(1) = 1 * bf(2) = 2 * bf(3) = 2 * bf(4) = 3 * ... and so on.
*/ #define bits_per(n) \
( \
__builtin_constant_p(n) ? ( \
((n) == 0 || (n) == 1) \
? 1 : ilog2(n) + 1 \
) : \
__bits_per(n) \
)
/** * max_pow_of_two_factor - return highest power-of-2 factor * @n: parameter * * find highest power-of-2 which is evenly divisible into n. * 0 is returned for n == 0 or 1.
*/ staticinline __attribute__((const)) unsignedint max_pow_of_two_factor(unsignedint n)
{ return n & -n;
}
#endif/* _LINUX_LOG2_H */
¤ Dauer der Verarbeitung: 0.30 Sekunden
(vorverarbeitet)
¤
Die Informationen auf dieser Webseite wurden
nach bestem Wissen sorgfältig zusammengestellt. Es wird jedoch weder Vollständigkeit, noch Richtigkeit,
noch Qualität der bereit gestellten Informationen zugesichert.
Bemerkung:
Die farbliche Syntaxdarstellung ist noch experimentell.
