Convert raw HEX to char

ErnieM said:

Sure you can define it as "static char" you get the improvement in instruction count, but pay a penalty in RAM as for some oddball reason C18 seems to put the static string into RAM. So bottom line is stash the string into ROM for the best efficiency.

Click to expand...

I mean add "static", not instead. That is, "static const char...". I'm shooting for two things here: 1) to keep the string inside the subroutine instead of splitting it off to a global somewhere else even though it only matters to the subroutine (yuck), and 2) to state it in a way that it would work for your pic and pretty much any C program in general. However, #2 is not such a big deal—it's just because this is a general programming forum and I was shooting for one statement that was generic C and would work for everyone. If it doesn't work for you, add "rom" as well ("static const rom char..."). I did download a lite IDE and compiler for C18 and it did seem to be happy with that. I couldn't figure out how to get a disassembly listing, though, to verify. It seemed to put it in rom for "static const char" as well, but the address was different and I couldn't figure out how to confirm it was in ROM or get an asm listing.

Now before you go thinking I did all this just to prove you wrong, what started me on this was looking to remove 1 or 2 bytes in the string definition: char foo[] = "1234"; is not 4 bytes but 5 as the trailing zero is strapped on the string. As in our case we don't need that zero I was looking at making an array: char foo[4] = {'1','2','3','4'};

Click to expand...

I think C is happy with

char foo[4] = "1234";

if you want to not store the trailing null. That is, I know it works, but I don't know offhand if that behavior is mandated in the standard.

Edit:

OK, I did figure out how to get a disassembly during debugging, though I couldn't figure out how to get the whole listing (just the current routine). It looks like it gets loaded into RAM as a static array (because I see the subroutine offset by 16 in memory) unless you add the "rom" qualifier (static const rom char hexchars[16] = "0123456789abcdef". The code itself gets one byte longer (TBLRD*). Anyway, the bottom line is that "static" saves you from making it global, and I don't think you give up anything else.