ilog2.h File Reference

Provide ilog2() function. More...

#include <stdint.h>
#include <zephyr/toolchain.h>
#include <zephyr/arch/common/ffs.h>
#include <zephyr/sys/util.h>

Go to the source code of this file.

Macros
#define	ilog2_compile_time_const_u32(n)
	Calculate the floor of log2 for compile time constant. More...
#define	ilog2(n)
	Calculate integer log2. More...

Detailed Description

Provide ilog2() function.

Macro Definition Documentation

ilog2

#define ilog2

(

n

)

Value:

        (                                               \
                __builtin_constant_p(n) ?               \
                ilog2_compile_time_const_u32(n) :       \
                find_msb_set(n) - 1                     \
        )

Calculate integer log2.

This calculates the floor of log2 (integer of log2).

Warning

Will return 0 if input value is 0, which is invalid for log2.

Parameters

n	Input value

Returns

Integer log2 of n

ilog2_compile_time_const_u32

#define ilog2_compile_time_const_u32

(

n

)

Value:

        (                                               \
                (n < 2) ? 0 :                           \
                ((n & BIT(31)) == BIT(31)) ? 31 :       \
                ((n & BIT(30)) == BIT(30)) ? 30 :       \
                ((n & BIT(29)) == BIT(29)) ? 29 :       \
                ((n & BIT(28)) == BIT(28)) ? 28 :       \
                ((n & BIT(27)) == BIT(27)) ? 27 :       \
                ((n & BIT(26)) == BIT(26)) ? 26 :       \
                ((n & BIT(25)) == BIT(25)) ? 25 :       \
                ((n & BIT(24)) == BIT(24)) ? 24 :       \
                ((n & BIT(23)) == BIT(23)) ? 23 :       \
                ((n & BIT(22)) == BIT(22)) ? 22 :       \
                ((n & BIT(21)) == BIT(21)) ? 21 :       \
                ((n & BIT(20)) == BIT(20)) ? 20 :       \
                ((n & BIT(19)) == BIT(19)) ? 19 :       \
                ((n & BIT(18)) == BIT(18)) ? 18 :       \
                ((n & BIT(17)) == BIT(17)) ? 17 :       \
                ((n & BIT(16)) == BIT(16)) ? 16 :       \
                ((n & BIT(15)) == BIT(15)) ? 15 :       \
                ((n & BIT(14)) == BIT(14)) ? 14 :       \
                ((n & BIT(13)) == BIT(13)) ? 13 :       \
                ((n & BIT(12)) == BIT(12)) ? 12 :       \
                ((n & BIT(11)) == BIT(11)) ? 11 :       \
                ((n & BIT(10)) == BIT(10)) ? 10 :       \
                ((n & BIT(9)) == BIT(9)) ? 9 :          \
                ((n & BIT(8)) == BIT(8)) ? 8 :          \
                ((n & BIT(7)) == BIT(7)) ? 7 :          \
                ((n & BIT(6)) == BIT(6)) ? 6 :          \
                ((n & BIT(5)) == BIT(5)) ? 5 :          \
                ((n & BIT(4)) == BIT(4)) ? 4 :          \
                ((n & BIT(3)) == BIT(3)) ? 3 :          \
                ((n & BIT(2)) == BIT(2)) ? 2 :          \
                1                                       \
        )

Calculate the floor of log2 for compile time constant.

This calculates the floor of log2 (integer log2) for 32-bit unsigned integer.

Note

This should only be used for compile time constant when value is known during preprocessing stage. DO NOT USE for runtime code due to the big tree of nested if-else blocks.

Warning

Will return 0 if input value is 0, which is invalid for log2.

Parameters

n	Input value

Returns

Integer log2 of