ccan/ilog.h

/* CC0 (Public domain) - see LICENSE file for details */
#if !defined(_ilog_H)
# define _ilog_H (1)
# include "config.h"
# include <stdint.h>
# include <limits.h>
# include <ccan/compiler.h>

/**
 * ilog32 - Integer binary logarithm of a 32-bit value.
 * @_v: A 32-bit value.
 * Returns floor(log2(_v))+1, or 0 if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * Note that many uses will resolve to the fast macro version instead.
 *
 * See Also:
 *	ilog32_nz(), ilog64()
 *
 * Example:
 *	// Rounds up to next power of 2 (if not a power of 2).
 *	static uint32_t round_up32(uint32_t i)
 *	{
 *		assert(i != 0);
 *		return 1U << ilog32(i-1);
 *	}
 */
int ilog32(uint32_t _v);

/**
 * ilog32_nz - Integer binary logarithm of a non-zero 32-bit value.
 * @_v: A 32-bit value.
 * Returns floor(log2(_v))+1, or undefined if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * Note that many uses will resolve to the fast macro version instead.
 * See Also:
 *	ilog32(), ilog64_nz()
 * Example:
 *	// Find Last Set (ie. highest bit set, 0 to 31).
 *	static uint32_t fls32(uint32_t i)
 *	{
 *		assert(i != 0);
 *		return ilog32_nz(i) - 1;
 *	}
 */
int ilog32_nz(uint32_t _v);

/**
 * ilog64 - Integer binary logarithm of a 64-bit value.
 * @_v: A 64-bit value.
 * Returns floor(log2(_v))+1, or 0 if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * Note that many uses will resolve to the fast macro version instead.
 * See Also:
 *	ilog64_nz(), ilog32()
 */
int ilog64(uint64_t _v);

/**
 * ilog64_nz - Integer binary logarithm of a non-zero 64-bit value.
 * @_v: A 64-bit value.
 * Returns floor(log2(_v))+1, or undefined if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * Note that many uses will resolve to the fast macro version instead.
 * See Also:
 *	ilog64(), ilog32_nz()
 */
int ilog64_nz(uint64_t _v);

/**
 * STATIC_ILOG_32 - The integer logarithm of an (unsigned, 32-bit) constant.
 * @_v: A non-negative 32-bit constant.
 * Returns floor(log2(_v))+1, or 0 if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * This macro should only be used when you need a compile-time constant,
 * otherwise ilog32 or ilog32_nz are just as fast and more flexible.
 *
 * Example:
 *	#define MY_PAGE_SIZE	4096
 *	#define MY_PAGE_BITS	(STATIC_ILOG_32(PAGE_SIZE) - 1)
 */
#define STATIC_ILOG_32(_v) (STATIC_ILOG5((uint32_t)(_v)))

/**
 * STATIC_ILOG_64 - The integer logarithm of an (unsigned, 64-bit) constant.
 * @_v: A non-negative 64-bit constant.
 * Returns floor(log2(_v))+1, or 0 if _v==0.
 * This is the number of bits that would be required to represent _v in two's
 *  complement notation with all of the leading zeros stripped.
 * This macro should only be used when you need a compile-time constant,
 * otherwise ilog64 or ilog64_nz are just as fast and more flexible.
 */
#define STATIC_ILOG_64(_v) (STATIC_ILOG6((uint64_t)(_v)))

/* Private implementation details */

/*Note the casts to (int) below: this prevents "upgrading"
   the type of an entire expression to an (unsigned) size_t.*/
#if INT_MAX>=2147483647 && HAVE_BUILTIN_CLZ
#define builtin_ilog32_nz(v) \
	(((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clz(v))
#elif LONG_MAX>=2147483647L && HAVE_BUILTIN_CLZL
#define builtin_ilog32_nz(v) \
	(((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clzl(v))
#endif

#if INT_MAX>=9223372036854775807LL && HAVE_BUILTIN_CLZ
#define builtin_ilog64_nz(v) \
	(((int)sizeof(unsigned)*CHAR_BIT) - __builtin_clz(v))
#elif LONG_MAX>=9223372036854775807LL && HAVE_BUILTIN_CLZL
#define builtin_ilog64_nz(v) \
	(((int)sizeof(unsigned long)*CHAR_BIT) - __builtin_clzl(v))
#elif HAVE_BUILTIN_CLZLL
#define builtin_ilog64_nz(v) \
	(((int)sizeof(unsigned long long)*CHAR_BIT) - __builtin_clzll(v))
#endif

#ifdef builtin_ilog32_nz
#define ilog32(_v) (builtin_ilog32_nz(_v)&-!!(_v))
#define ilog32_nz(_v) builtin_ilog32_nz(_v)
#else
#define ilog32_nz(_v) ilog32(_v)
#define ilog32(_v) (IS_COMPILE_CONSTANT(_v) ? STATIC_ILOG_32(_v) : ilog32(_v))
#endif /* builtin_ilog32_nz */

#ifdef builtin_ilog64_nz
#define ilog64(_v) (builtin_ilog64_nz(_v)&-!!(_v))
#define ilog64_nz(_v) builtin_ilog64_nz(_v)
#else
#define ilog64_nz(_v) ilog64(_v)
#define ilog64(_v) (IS_COMPILE_CONSTANT(_v) ? STATIC_ILOG_64(_v) : ilog64(_v))
#endif /* builtin_ilog64_nz */

/* Macros for evaluating compile-time constant ilog. */
# define STATIC_ILOG0(_v) (!!(_v))
# define STATIC_ILOG1(_v) (((_v)&0x2)?2:STATIC_ILOG0(_v))
# define STATIC_ILOG2(_v) (((_v)&0xC)?2+STATIC_ILOG1((_v)>>2):STATIC_ILOG1(_v))
# define STATIC_ILOG3(_v) \
 (((_v)&0xF0)?4+STATIC_ILOG2((_v)>>4):STATIC_ILOG2(_v))
# define STATIC_ILOG4(_v) \
 (((_v)&0xFF00)?8+STATIC_ILOG3((_v)>>8):STATIC_ILOG3(_v))
# define STATIC_ILOG5(_v) \
 (((_v)&0xFFFF0000)?16+STATIC_ILOG4((_v)>>16):STATIC_ILOG4(_v))
# define STATIC_ILOG6(_v) \
 (((_v)&0xFFFFFFFF00000000ULL)?32+STATIC_ILOG5((_v)>>32):STATIC_ILOG5(_v))

#endif /* _ilog_H */