125 lines
3.6 KiB
Go
125 lines
3.6 KiB
Go
package encoding
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import (
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"bytes"
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"fmt"
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"log"
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)
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type GSM7Coder struct{}
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func (c *GSM7Coder) Encode(s string, buf *bytes.Buffer) error {
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// utf8 := *(*[]byte)(unsafe.Pointer(&s))
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utf8 := []byte(s)
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var (
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offset int = 1
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bitshift byte = 0
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leap, shift bool
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)
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for index, septet := range utf8 {
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if septet > 0b01111111 {
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return fmt.Errorf("invalid character at index %d", index)
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}
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if index == 0 {
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continue
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}
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bitshift++
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// 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)
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mask := byte(255 >> (8 - bitshift))
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masked := (mask & septet) << (8 - bitshift)
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// log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d Mask:%08b Masked:%08b", index, offset, bitshift, mask, masked)
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if leap {
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masked >>= 1
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}
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utf8[index-offset] |= masked
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utf8[index] >>= bitshift
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if !leap {
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buf.WriteByte(utf8[index-offset])
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}
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if index == len(utf8)-1 && utf8[index] > 0 {
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buf.WriteByte(utf8[index])
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}
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// 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)
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if bitshift >= 7 {
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if leap {
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// log.Printf("Shift at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
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leap = false
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bitshift = 0
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offset++
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shift = true
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continue
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}
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// log.Printf("Leap at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
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leap = true
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bitshift = 6
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}
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if shift {
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offset = 1
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}
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}
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return nil
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}
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func (c *GSM7Coder) Decode(buf *bytes.Buffer) (string, error) {
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gsm7 := buf.Bytes()
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var (
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output []byte = make([]byte, len(gsm7)*8/7)
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offset int = (len(gsm7) / 8) + 1
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bitshift byte = 0
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leap, shift bool
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)
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log.Println(len(output))
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for index := len(gsm7) - 2; index >= 0; index-- {
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octet := gsm7[index]
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bitshift = byte((index + 1) % 8)
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if bitshift == 7 {
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leap = true
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}
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log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) Output(%-3d):%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], index+offset, output[index+offset], output[index+offset], leap)
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mask := byte(255 << (8 - bitshift))
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masked := (mask & octet) >> (8 - bitshift)
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log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d Mask:%08b Masked:%08b", index, offset, bitshift, mask, masked)
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output[index+offset] |= masked
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continue
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gsm7[index+offset] |= masked
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gsm7[index] <<= bitshift
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if !leap {
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buf.WriteByte(gsm7[index+offset])
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}
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if index == len(gsm7)-1 && gsm7[index] > 0 {
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buf.WriteByte(gsm7[index])
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}
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log.Printf("Index:%-3d Offset:%-3d Bitshift:%-3d CurrentByte:%08b (%-3d) OffsetByte:%08b (%-3d) Leap:%5v", index, offset, bitshift, gsm7[index], gsm7[index], gsm7[index-offset], gsm7[index-offset], leap)
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if bitshift >= 7 {
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if leap {
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log.Printf("Shift at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
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leap = false
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bitshift = 0
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offset++
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shift = true
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continue
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}
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log.Printf("Leap at Index:%-3d Offset:%-3d Bitshift:%-3d", index, offset, bitshift)
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leap = true
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bitshift = 6
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}
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if shift {
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offset = 1
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}
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}
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return "", nil
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}
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// Allocation free
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// Which means data MUST have space for value
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func InsertAt(data *[]byte, index int, value byte) {
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copy((*data)[index+1:], (*data)[index:])
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(*data)[index] = value
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}
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