log2.h File Reference

#include <stdint.h>

Go to the source code of this file.

Macros
#define	const_ilog2(n)
	const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value : parameter More...
#define	ilog2(n)
	ilog2 - log base 2 of 32-bit or a 64-bit unsigned value : parameter More...

Functions
static	__attribute__ ((always_inline)) int fls(unsigned int x)
	fls - find last (most-significant) bit set @x: the word to search More...
static	__attribute__ ((const)) int __ilog2_u32(uint32_t n)

Macro Definition Documentation

const_ilog2

#define const_ilog2

(

n

)

const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
: parameter

Use this where sparse expects a true constant expression, e.g. for array indices.

ilog2

#define ilog2

(

n

)

Value:

( \
        __builtin_constant_p(n) ?       \
        const_ilog2(n) :                \
        (sizeof(n) <= 4) ?              \
        __ilog2_u32(n) :                \
        __ilog2_u64(n)                  \
 )

ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
: 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)

Function Documentation

__attribute__() [1/2]

static __attribute__ ( (always_inline)  )

inlinestatic

fls - find last (most-significant) bit set @x: the word to search

fls64 - find last set bit in a 64-bit word @x: the word to search

This is defined the same way as ffs. Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.

This is defined in a similar way as the libc and compiler builtin ffsll, but returns the position of the most significant set bit.

fls64(value) returns 0 if value is 0 or the position of the last set bit if value is nonzero. The last (most significant) bit is at position 64.

References x.

__attribute__() [2/2]

static __attribute__ ( (const)  )

inlinestatic

References n.