log2.h File Reference

#include <linux/types.h>
#include <linux/bitops.h>

Go to the source code of this file.

Macros
#define	ilog2(n)
#define	roundup_pow_of_two(n)
#define	rounddown_pow_of_two(n)
#define	order_base_2(n)   ilog2(roundup_pow_of_two(n))

Functions
	__attribute__ ((const, noreturn)) int ____ilog2_NaN(void)

Macro Definition Documentation

#define ilog2

(

n

)

ilog2 - log of 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)

Definition at line 85 of file log2.h.

#define order_base_2

(

n

)

ilog2(roundup_pow_of_two(n))

order_base_2 - calculate the (rounded up) base 2 order of the argument
: 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.

Definition at line 206 of file log2.h.

#define rounddown_pow_of_two

(

n

)

Value:

(                       \
    __builtin_constant_p(n) ? (     \
        (1UL << ilog2(n))) :        \
    __rounddown_pow_of_two(n)       \
 )

rounddown_pow_of_two - round the given value down to nearest power of two
- 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

Definition at line 185 of file log2.h.

#define roundup_pow_of_two

(

n

)

Value:

(                       \
    __builtin_constant_p(n) ? (     \
        (n == 1) ? 1 :          \
        (1UL << (ilog2((n) - 1) + 1))   \
                   ) :      \
    __roundup_pow_of_two(n)         \
 )

roundup_pow_of_two - round the given value up to nearest power of two
- 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

Definition at line 168 of file log2.h.

Function Documentation

__attribute__

(

(const, noreturn)

)