Difference between revisions of "Common data type ranges"

Latest revision as of 12:11, 24 November 2017

TODO: This is just some notes for me to reference at the moment, please only use these IF YOU KNOW THEY APPLY - there are various C conventions...

In general, given [ilmath]n[/ilmath] bits, the range of [ilmath]x[/ilmath] (an [ilmath]n[/ilmath]-bit signed two's complement integer) is:
- [ilmath]-2^{n-1} \le x \le 2^{n-1}-1[/ilmath], which we may write as a closed interval of the integers, [ilmath]x\in[-2^{n-1},\ 2^{n-1}-1][/ilmath]

Bits	Range (inclusive)				Comment
	Signed		Unsigned
	Low	High	Low	High
8	-128	127	0	255
16	-32,768	32,767	0	65,365	Often associated with older spreadsheet software, only supporting rows from 1 to 65,536. Note the offset^{[Note 1]}.
24	-8,388,608	8,388,607	0	16,777,215	Relevant for float - per standard.
32	-2,147,483,648	2,147,483,647	0	4,294,967,295	Notice that 2,147,483,647 is about 68.05 years^{[Note 2]}, and 1970+68=2038 - see 2038 problem
64	-9,223,372,036,854,775,808	9,223,372,036,854,775,807	0	18,446,744,073,709,551,615	9.2 billion trillion, 18.4 billion trillion using 10^3 increments.

TODO: Notice the lowest digit of each column is the same. Why?

↑ Internally for rows they'd have used shorts for the job, adding one to the displayed row number as spreadsheets have no row 0.
↑
Calculation:
- [math]A:\eq\frac{2^{31} -1}{60*60*24*365.25}\approx 68.04965039[/math] which is 68 years and [ilmath](A-68)*365.25\approx 18.135[/ilmath], so:
Approximately 68 years and 18 days after the first instant of 1970 (UTC) is the maximum time a signed 4 byte integer can represent