Sign extensionPascal Cuoq - 25th Apr 2013
There is no “sign extension” in C. Please stop referring to “sign extension” in C programs.
In assembly, there is such a thing as “sign extension”
Sign-extend is an assembly instruction say
movsx %al %ebx to transfer the contents of a narrow register say
%al to a wide register say
%ebx copying the most significant bit of the narrow register all over the unoccupied bits of the wide register.
In C there is no “sign extension”. Really.
In C a
-3 and the contents of that variable is transferred to another variable of type
int like so:
int i = s;
-3. That's it. That's “sign extension”.
It's an assignment and in this particular case a promotion. With other types it could have been a conversion. The target wide variable receives the value that was contained in the narrow variable. Why would this operation need a name and such an ugly name as “sign extension” at that?
The name for “sign extension” in C is “getting the value”. Variable
i receives the value of
s. That's it. That is all there is.