initial commit

Author: petoc

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2020 Peter C.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,59 @@
+# Algorithms
+
+Collection of algorithm implementations for Go.
+
+## Error detection
+
+[Damm](https://github.com/petoc/algo/tree/master/damm)<br>
+[Damm64](https://github.com/petoc/algo/tree/master/damm64) (using quasigroups for character base from 3 to 64 characters)<br>
+[Luhn](https://github.com/petoc/algo/tree/master/luhn)<br>
+
+
+## Usage
+
+### Damm
+
+Implementation of error detection algorithm for numeric codes from H. Michael Damm.
+
+```go
+import "github.com/petoc/algo/damm"
+```
+
+```go
+damm.Calculate("123456789") // 4
+damm.Validate("1234567894") // true
+```
+
+### Damm64
+
+Based on error detection algorithm from H. Michael Damm. Uses pre-generated quasigroups for character base from 3 to 64 characters.
+
+```go
+import "github.com/petoc/algo/damm64"
+```
+
+```go
+base := "0123456789ABCDEFGHIJKLMNOPQRSTUV"
+damm64.Calculate(base, "G12Q") // F
+damm64.Validate(base, "G12QF") // true
+```
+### Luhn
+
+Implementation of error detection algorithm for numeric codes from Hans Peter Luhn.
+
+```go
+import "github.com/petoc/algo/luhn"
+```
+
+```go
+luhn.Calculate("123456789") // 7
+luhn.Validate("1234567897") // true
+```
+
+## Sources
+
+Damm Quasigroups (http://www.md-software.de/math/DAMM_Quasigruppen.txt)
+
+## License
+
+Licensed under MIT license.

damm/damm.go

@@ -0,0 +1,36 @@
+package damm
+
+var table = [100]int8{
+	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,
+}
+
+func id(i, d int8) int8 {
+	return table[i*10+d]
+}
+
+// Calculate ...
+func Calculate(s string) int8 {
+	var i int8
+	for _, r := range s[:] {
+		d := int8(r - '0')
+		if d < 0 || d > 9 {
+			return -1
+		}
+		i = id(i, d)
+	}
+	return i
+}
+
+// Validate ...
+func Validate(s string) bool {
+	return Calculate(s) == 0
+}

damm/damm_test.go

@@ -0,0 +1,28 @@
+package damm
+
+import (
+	"testing"
+)
+
+func TestDamm(t *testing.T) {
+	tt := map[string]bool{
+		"1234567890": false,
+		"1234567894": true,
+		"2345678945": true,
+		"3456789452": true,
+		"4567894520": false,
+	}
+	for s, e := range tt {
+		c := int8(s[len(s)-1] - '0')
+		r := Calculate(s[0 : len(s)-1])
+		if (c == r) != e {
+			t.Errorf("%s: expected %v, got %v", s, c, r)
+			return
+		}
+		g := Validate(s)
+		if g != e {
+			t.Errorf("%s: expected %v, got %v", s, e, g)
+			return
+		}
+	}
+}