Last week: Reversed Binary Numbers
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I started with a straightforward solution in PHP, using built-in functions:
function revert(int $input) : int
{
return (int)bindec(strrev(decbin($input)));
}
That was quick (good, because I had little time), but boring. So the next time, I decided to go for a solution with bitwise operations. The result:
function revert(int $input) : int
{
$result = 0;
$exponent = bitLength($input);
do {
--$exponent;
$lastBitValue = $input & 1;
$result += $lastBitValue * 2**$exponent;
} while ($input>>=1);
return $result;
}
function bitLength(int $input) : int
{
$result = 0;
do {
++$result;
} while ($input>>=1);
return $result;
}
I extracted the bitLenght function early, when I noticed that I would need it, then tested that one seperately. Just as in the Print Diamond kata, it helped to develop and test parts of the algorithm separately.
Finally, I did the Kata again in Go, following the same approach.
Full code with test:
reverse.go
package reversebinary
func Reverse(i uint) (rev uint) {
for len := Length(i); len > 0; len-- {
bit := i & 1
rev += bit * (1 << (len - 1))
i>>=1
}
return
}
func Length(i uint) (len uint) {
if (i == 0) {
return 1
}
for len = 0; i > 0; len++ {
i>>=1
}
return
}
reverse_test.go
package reversebinary
import "testing"
func TestLength(t *testing.T) {
cases := []struct {
in, want uint
}{
{0, 1},
{1, 1},
{2, 2},
{3, 2},
{7, 3},
{8, 4},
}
for _, c := range cases {
got := Length(c.in)
if got != c.want {
t.Errorf("Length(%v) == %v, want %v", c.in, got, c.want)
}
}
}
func TestReverse(t *testing.T) {
cases := []struct {
in, want uint
}{
{0, 0},
{1, 1},
{2, 1},
{3, 3},
{11, 13},
{61, 47},
}
for _, c := range cases {
got := Reverse(c.in)
if got != c.want {
t.Errorf("Reverse(0b%b) == 0b%b, want 0b%b", c.in, got, c.want)
}
}
}
Twelvth Kata: Ugly Trivia Game
The purpose of a legacy code kata is to practice adding test coverage to previously untested code and to clean up the code without breaking it. This kata in perticular should be tacked with a golden master test (a.k.a. characterization test or scaffolding test). The legacy code can be found at https://github.com/jbrains/trivia
The original description of the kata can be found at http://kata-log.rocks/ugly-trivia-kata.
Since this is a bigger task, my plan is to tackle the PHP version once, in multiple steps.
