On Thursday, 9 February 2017 at 18:34:30 UTC, Era Scarecrow wrote:
On Thursday, 9 February 2017 at 17:36:11 UTC, Nestor wrote:
I was trying to port C code from the article in Wikiversity
[1] to D, but I'm not sure this implementation is the most
efficient way to do it in D, so suggestions to optimize it are
welcome:
import std.stdio;
static immutable char[] QG10Matrix =
"03175986427092154863420687135917509834266123045978" ~
"36742095815869720134894536201794386172052581436790";
char checkDigit(string str) {
char tmpdigit = '0';
foreach(chr; str) tmpdigit = QG10Matrix[(chr - '0') +
(tmpdigit - '0') * 10];
return tmpdigit;
}
Well one thing is you can probably reduce them from chars to
just bytes, instead of having to subtract you can instead add
at the end. Although unless you're working with a VERY large
input you won't see a difference.
Actually since you're also multiplying by 10, you can
incorporate that in the table too... (although a mixin might be
better for the conversion than by hand)
static immutable char[] QG10Matrix = [
00,30,10,70,50,90,80,60,40,20,
70,00,90,20,10,50,40,80,60,30,
40,20,00,60,80,70,10,30,50,90,
10,70,50,00,90,80,30,40,20,60,
60,10,20,30,00,40,50,90,70,80,
30,60,70,40,20,00,90,50,80,10,
50,80,60,90,70,20,00,10,30,40,
80,90,40,50,30,60,20,00,10,70,
90,40,30,80,60,10,70,20,00,50,
20,50,80,10,40,30,60,70,90,00];
char checkDigit(string str) {
char tmpdigit = 0;
foreach(chr; str) tmpdigit = QG10Matrix[(chr - '0') +
tmpdigit];
return (tmpdigit/10) + '0';
}
OK I changed the approach using a multidimensional array for the
matrix so I could ditch arithmetic operations altogether, but
curiously after measuring a few thousand runs of both
implementations through avgtime, I see no noticeable difference.
Why?
import std.stdio;
static immutable ubyte[][] QG10Matrix = [
[0,3,1,7,5,9,8,6,4,2],[7,0,9,2,1,5,4,8,6,3],
[4,2,0,6,8,7,1,3,5,9],[1,7,5,0,9,8,3,4,2,6],
[6,1,2,3,0,4,5,9,7,8],[3,6,7,4,2,0,9,5,8,1],
[5,8,6,9,7,2,0,1,3,4],[8,9,4,5,3,6,2,0,1,7],
[9,4,3,8,6,1,7,2,0,5],[2,5,8,1,4,3,6,7,9,0],
];
static int charToInt(char chr) {
scope(failure) return -1;
return cast(int)(chr - '0');
}
ubyte checkDigit(string str) {
ubyte tmpdigit;
foreach(chr; str) tmpdigit =
QG10Matrix[tmpdigit][charToInt(chr)];
return tmpdigit;
}
enum {
EXIT_SUCCESS = 0,
EXIT_FAILURE = 1,
}
int main(string[] args) {
scope(failure) {
writeln("Invalid arguments. You must pass a number.");
return EXIT_FAILURE;
}
assert(args.length == 2);
ubyte digit = checkDigit(args[1]);
if(digit == 0) writefln("%s is a valid number.", args[1]);
else {
writefln("%s is not a valid number (but it would be,
appending digit %s).",
args[1], digit);
}
return EXIT_SUCCESS;
}
