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151 lines (138 loc) · 5.3 KB
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/* 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/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) CONST_FUNCTION;
/**
* 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) CONST_FUNCTION;
/**
* 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) CONST_FUNCTION;
/**
* 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) CONST_FUNCTION;
/**
* 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 */