hi

lexnum.go

@@ -0,0 +1,149 @@
+package lexnum
+
+import (
+	"fmt"
+	"strconv"
+)
+
+type Encoder struct {
+	pos rune
+	neg rune
+}
+
+func NewEncoder(pos rune, neg rune) *Encoder {
+	if pos < neg {
+		panic("positive lexnum rune must be of higher rank than negative lexnum rune")
+	}
+	return &Encoder{pos: pos, neg: neg}
+}
+
+func (l Encoder) EncodeInt(i int) string {
+	if i == 0 {
+		return "0"
+	}
+	if i > 0 {
+		return l.encodePos(i)
+	}
+	return l.encodeNeg(i)
+}
+
+func (l Encoder) encodePos(i int) string {
+	s := strconv.Itoa(i)
+	if len(s) == 1 {
+		return fmt.Sprintf("%c%s", l.pos, s)
+	}
+	return fmt.Sprintf("%c%s%s", l.pos, l.encodePos(len(s)), s)
+}
+
+func (l Encoder) encodeNeg(i int) string {
+	if i < 0 {
+		i = -i
+	}
+	runes := []rune(strconv.Itoa(i))
+	for i := range runes {
+		runes[i] = l.flip(runes[i])
+	}
+	if len(runes) == 1 {
+		return fmt.Sprintf("%c%s", l.neg, string(runes))
+	}
+	return fmt.Sprintf("%c%s%s", l.neg, l.encodeNeg(len(runes)), string(runes))
+}
+
+func (l Encoder) flip(r rune) rune {
+	switch r {
+	case '0':
+		return '9'
+	case '1':
+		return '8'
+	case '2':
+		return '7'
+	case '3':
+		return '6'
+	case '4':
+		return '5'
+	case '5':
+		return '4'
+	case '6':
+		return '3'
+	case '7':
+		return '2'
+	case '8':
+		return '1'
+	case '9':
+		return '0'
+	default:
+		panic(fmt.Sprintf("can't flip illegal rune %c", r))
+	}
+}
+
+func (l Encoder) flipInPlace(runes []rune) {
+	for i := range runes {
+		runes[i] = l.flip(runes[i])
+	}
+}
+
+func (l Encoder) isDigit(r rune) bool {
+	return r >= '0' && r <= '9'
+}
+
+func (l Encoder) prefixCount(runes []rune) int {
+	i := 0
+	for _, r := range runes {
+		if r == l.neg || r == l.pos {
+			i++
+		} else {
+			break
+		}
+	}
+	return i
+}
+
+func (l Encoder) DecodeInt(s string) (int, error) {
+	if s == "" {
+		return 0, fmt.Errorf("illegal Lexnum decode of empty string")
+	}
+	runes := []rune(s)
+	if len(runes) == 1 {
+		if runes[0] == '0' {
+			return 0, nil
+		}
+		return 0, fmt.Errorf("illegal Lexnum decode of non-zero unit string: %s", s)
+	}
+	switch runes[0] {
+	case l.neg:
+		return l.decodeNeg(runes)
+	case l.pos:
+		return l.decodePos(runes)
+	default:
+		return 0, fmt.Errorf("illegal Lexnum decode of string without %c or %c as initial rune: %s", l.neg, l.pos, s)
+	}
+}
+
+func (l Encoder) decodePos(runes []rune) (int, error) {
+	return l._decodePos(runes, 1, l.prefixCount(runes))
+}
+
+func (l Encoder) _decodePos(runes []rune, size int, index int) (int, error) {
+	n, err := strconv.ParseInt(string(runes[index:index+size]), 10, 64)
+	if err != nil {
+		return 0, err
+	}
+	if index+size > len(runes) {
+		return 0, fmt.Errorf("illegal Lexnum decode of abnormally long string %s", string(runes))
+	}
+	if index+size == len(runes) {
+		return int(n), nil
+	}
+	return l._decodePos(runes, int(n), index+size)
+
+}
+
+func (l Encoder) decodeNeg(runes []rune) (int, error) {
+	p := l.prefixCount(runes)
+	l.flipInPlace(runes[p:len(runes)])
+	n, err := l._decodePos(runes, 1, p)
+	if err != nil {
+		return 0, err
+	}
+	return -n, nil
+}

lexnum_test.go

@@ -0,0 +1,77 @@
+package lexnum
+
+import (
+	"math/rand"
+	"sort"
+	"testing"
+	"time"
+)
+
+var lexNumTests = []struct {
+	in  int
+	out string
+}{
+	{0, "0"},
+	{1, "x1"},
+	{9, "x9"},
+	{10, "xx210"},
+	{99, "xx299"},
+	{100, "xx3100"},
+	{12345, "xx512345"},
+	{123456789, "xx9123456789"},
+	{1234567890, "xxx2101234567890"},
+	{-1, "o8"},
+	{-2, "o7"},
+	{-9, "o0"},
+	{-10, "oo789"},
+	{-11, "oo788"},
+	{-123, "oo6876"},
+	{-123456789, "oo0876543210"},
+	{-1234567890, "ooo7898765432109"},
+}
+
+func TestLexnum(t *testing.T) {
+	rand.Seed(time.Now().UnixNano())
+    e := NewEncoder('x', 'o')
+	for _, test := range lexNumTests {
+		s := e.EncodeInt(test.in)
+		t.Logf("%d -> %s", test.in, test.out)
+		if s != test.out {
+			t.Errorf("encode input: %v, output: %v, expected output: %v", test.in, s, test.out)
+		}
+		n, err := e.DecodeInt(s)
+		if err != nil {
+			t.Errorf("decode error: %v", err)
+			continue
+		}
+		if n != test.in {
+			t.Errorf("decode input: %v, output: %v, expected output: %v", s, n, test.in)
+		}
+	}
+
+	runsize := 8
+	for runz := 0; runz < 4; runz += 1 {
+		nums, stringz := make([]int, runsize), make([]string, runsize)
+		for i := 0; i < runsize; i++ {
+			nums[i] = rand.Int()
+			if rand.Int()%2 == 0 {
+				nums[i] = -nums[i]
+			}
+			stringz[i] = e.EncodeInt(nums[i])
+		}
+		sort.Strings(stringz)
+		sort.Ints(nums)
+		t.Logf("stringz sorted: %v", stringz)
+		t.Logf("nums sorted: %v", nums)
+		for i := 0; i < runsize; i++ {
+			n, err := e.DecodeInt(stringz[i])
+			if err != nil {
+				t.Errorf("unable to decode our own input: %v", stringz[i])
+				continue
+			}
+			if n != nums[i] {
+				t.Errorf("sorting is broken")
+			}
+		}
+	}
+}