Question

I want to create my own time stamp data structure in C.

DAY ( 0 – 30 ), HOUR ( 0 – 23 ), MINUTE ( 0 – 59 )

What is the smallest data structure possible?

Answer 1

Well, you could pack it all in an unsigned short (That’s 2 bytes, 5 bits for Day, 5 bits for hour, 6 bits for minute)… and use some shifts and masking to get the values.

unsigned short timestamp = <some value>; // Bits: DDDDDHHHHHMMMMMM  int day = (timestamp >> 11) & 0x1F; int hour = (timestamp >> 6) & 0x1F; int min = (timestamp) & 0x3F;  unsigned short dup_timestamp = (short)((day << 11) | (hour << 6) | min);  

or using macros

#define DAY(x)    (((x) >> 11) & 0x1F) #define HOUR(x)   (((x) >> 6)  & 0x1F) #define MINUTE(x) ((x)         & 0x3F) #define TIMESTAMP(d, h, m) ((((d) & 0x1F) << 11) | (((h) & 0x1F) << 6) | ((m) & 0x3F) 

(You didn’t mention month/year in your current version of the question, so I’ve omitted them).

[Edit: use unsigned short – not signed short.]