MRZ (Machine Readable Zone) checksum calculator

mrz.d

import std.algorithm;
import std.range;

ubyte charCode(dchar c) pure {
    switch (c) {
        case '<': return 0;
        case 'A': .. case 'Z': return cast(ubyte)(c - 'A' + 10);
        case '0': .. case '9': return cast(ubyte)(c - '0');
        default: assert(0);
    }
}

static assert(charCode('Z') == 35);
static assert(charCode('9') == 9);

int calcMrz(string data) pure {
    return data
        .map!(charCode)
        .zip([7,3,1].cycle)
        .fold!( (a,b) => a + b[0]*b[1] )(0) % 10;
}

static assert(calcMrz("AB2134<<<") == 5);

string calcField(string data) pure {
    return data ~ cast(char)('0' + calcMrz(data));
}

static assert(calcField("140910") == "1409105");


void main(string[] args) {
    import std.stdio;

    writeln(args[1..$]
        .map!(calcField)
        .fold!( (a,b) => a~b )
        .calcField
        );
}