helper program to cross check correctness of ffs with simpler algorithm

gen_ffs.zig

const std = @import("std");
const maxInt = std.math.maxInt;
const print = std.debug.print;

test "print ffs" {
    //var in: u64 = 0;
    //var in: u32 = 256;
    //var in: u64 = 256;
    var in: u128 = 256;
    var x: @TypeOf(in) = 0;
    var out: @TypeOf(in) = 0;

    print("\n", .{});
    //while (in <= 0xff) : (in += 1) {
    while (in < maxInt(@TypeOf(in))) : (in = @mulWithSaturation(in, 2)) {
        x = in; // must use temporary for correct iteration
        out = 0;

        // ffs - find first set
        var index: u32 = 0;
        if (x != 0) {
            while (((~x) & 1) != 0) {
                x = x >> 1;
                index += 1;
            }
        }
        //const one: @TypeOf(in) = 1;
        //out = one << index;
        out = index;

        //print("{d:>40}", .{in});
        print(" {x:>35}", .{in});
        //print(" {b:>32}", .{in});
        print(" {d:>5}\n", .{out}); //result
    }
}