Fix packing for larger strings

encoding/gsm7.go

@@ -7,34 +7,72 @@ import (
 
 type GSM7Coder struct{}
 
-
 func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
 	// utf8 := *(*[]byte)(unsafe.Pointer(&s))
 	utf8 := []byte(s)
-	var offset byte = 1
+	var offset int = 1
-	var bitshift byte = 1
+	var bitshift byte = 0
+	var leap, shift bool
 
 	for index, septet := range utf8 {
 		if septet > 0b01111111 {
 			return fmt.Errorf("invalid character at index %d", index)
 		}
-		bindex := byte(index)
+		if index == 0 {
-		if bindex == 0 {
 			continue
 		}
+		bitshift++
+		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte:%08b (%-3d) Leap:%5v", index, offset, bitshift, utf8[index], utf8[index], utf8[index-offset], utf8[index-offset], leap)
 		mask := byte(255 >> (8 - bitshift))
 		masked := (mask & septet) << (8 - bitshift)
-		utf8[bindex-offset] |= masked
+		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d Mask:%08b Masked:%08b", index, offset, bitshift, mask, masked)
-		utf8[bindex] >>= bitshift
+		if leap {
+			masked >>= 1
+		}
+		utf8[index-offset] |= masked
+		utf8[index] >>= bitshift
 
-		buf.WriteByte(utf8[bindex-offset])
+		if !leap {
-		bitshift++
+			buf.WriteByte(utf8[index-offset])
-		if bitshift == 8 {
+		}
-			offset++
+		if index == len(utf8)-1 && utf8[index] > 0 {
-			bitshift = 1
+			buf.WriteByte(utf8[index])
+		}
+		// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte:%08b (%-3d) Leap:%5v", index, offset, bitshift, utf8[index], utf8[index], utf8[index-offset], utf8[index-offset], leap)
+		if bitshift >= 7 {
+			if leap {
+				// log.Printf("Shift at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
+				leap = false
+				bitshift = 0
+				offset++
+				shift = true
+				continue
+			}
+			// log.Printf("Leap at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
+			leap = true
+			bitshift = 6
+		}
+		if shift {
+			offset = 1
 		}
 	}
 	return nil
+	// The issue happens during leap
+	// 2024/07/28 16:56:12 Index  7  1  7 11100100 00000000
+	// 2024/07/28 16:56:12 Leap at  7  1  7
+	// 2024/07/28 16:56:12 Index  8  1  7 11000010 00000000
+	// 2024/07/28 16:56:12 Shift at  8  1  7
+	// 2024/07/28 16:56:12 Index  9  2  1 11000010 00111100
+
+	// The correct output should be:
+	// Index  9  2  1 11100001 00111100
+
+	// Also
+	// 2024/07/28 16:58:49 Index  8  1  7 00000000 01100001
+	// 2024/07/28 16:58:49 Index  8  1  7 11000010 00000000
+	// 2024/07/28 16:58:49 Shift at  8  1  7
+	// 2024/07/28 16:58:49 Index  9  2  1 11000010 01111001
+	// 2024/07/28 16:58:49 Index  9  2  1 11000010 00111100 <-- the LSB 1 that is removed is not added to the previous byte (should be 11100001, not 11000010)
 }
 
 func (c *GSM7Coder) Decode(buf *bytes.Buffer) (string, error) {