Split uint16_t in bits in C

Question

Hello I have a uint16_t number and I need to split it in 3 parts.

The first 5 bits of this number gives me the hour.

The next 6 bits of this number gives me the minutes.

The next 5 bits of this number gives me the seconds.

So I need to split it in those 3 parts to get the info I need.

any idea ?

Answer 1

Leaving aside that you can't split 8 bits into 16 (I'm going to assume you actually have a uint16_t, since that makese sense here), what you want to is called a mask. Let's say your 16 bit value is stored in variable "value"

To get the first (most significant) 5 bits, you'd use the mask 0xF800, which in binary is 1111100000000000.

You use a bitwise AND to apply this:

    const uint16_t MASK;
    uint16_t value = whatever_was_passed_in;
    value = value & MASK;

This zeros out the bits you aren't interested in. If you want those bits shifted down to the lowest part of the variable, you can do that with a right shift:

    value = (value & MASK) >> 11;

The other chuncks are handled with the same process, but different masks and shift values.

Answer 2

typedef struct bit_time {
   unsigned int hour:5;
   unsigned int minute:6;
   unsigned int seconds:5;
} bit_time_t;

Here's a good explanation.