mirror of https://github.com/mindoc-org/mindoc.git
104 lines
2.1 KiB
Go
104 lines
2.1 KiB
Go
package ber
|
|
|
|
import (
|
|
"errors"
|
|
"fmt"
|
|
"io"
|
|
"math"
|
|
)
|
|
|
|
func readIdentifier(reader io.Reader) (Identifier, int, error) {
|
|
identifier := Identifier{}
|
|
read := 0
|
|
|
|
// identifier byte
|
|
b, err := readByte(reader)
|
|
if err != nil {
|
|
if Debug {
|
|
fmt.Printf("error reading identifier byte: %v\n", err)
|
|
}
|
|
return Identifier{}, read, err
|
|
}
|
|
read++
|
|
|
|
identifier.ClassType = Class(b) & ClassBitmask
|
|
identifier.TagType = Type(b) & TypeBitmask
|
|
|
|
if tag := Tag(b) & TagBitmask; tag != HighTag {
|
|
// short-form tag
|
|
identifier.Tag = tag
|
|
return identifier, read, nil
|
|
}
|
|
|
|
// high-tag-number tag
|
|
tagBytes := 0
|
|
for {
|
|
b, err := readByte(reader)
|
|
if err != nil {
|
|
if Debug {
|
|
fmt.Printf("error reading high-tag-number tag byte %d: %v\n", tagBytes, err)
|
|
}
|
|
return Identifier{}, read, err
|
|
}
|
|
tagBytes++
|
|
read++
|
|
|
|
// Lowest 7 bits get appended to the tag value (x.690, 8.1.2.4.2.b)
|
|
identifier.Tag <<= 7
|
|
identifier.Tag |= Tag(b) & HighTagValueBitmask
|
|
|
|
// First byte may not be all zeros (x.690, 8.1.2.4.2.c)
|
|
if tagBytes == 1 && identifier.Tag == 0 {
|
|
return Identifier{}, read, errors.New("invalid first high-tag-number tag byte")
|
|
}
|
|
// Overflow of int64
|
|
// TODO: support big int tags?
|
|
if tagBytes > 9 {
|
|
return Identifier{}, read, errors.New("high-tag-number tag overflow")
|
|
}
|
|
|
|
// Top bit of 0 means this is the last byte in the high-tag-number tag (x.690, 8.1.2.4.2.a)
|
|
if Tag(b)&HighTagContinueBitmask == 0 {
|
|
break
|
|
}
|
|
}
|
|
|
|
return identifier, read, nil
|
|
}
|
|
|
|
func encodeIdentifier(identifier Identifier) []byte {
|
|
b := []byte{0x0}
|
|
b[0] |= byte(identifier.ClassType)
|
|
b[0] |= byte(identifier.TagType)
|
|
|
|
if identifier.Tag < HighTag {
|
|
// Short-form
|
|
b[0] |= byte(identifier.Tag)
|
|
} else {
|
|
// high-tag-number
|
|
b[0] |= byte(HighTag)
|
|
|
|
tag := identifier.Tag
|
|
|
|
highBit := uint(63)
|
|
for {
|
|
if tag&(1<<highBit) != 0 {
|
|
break
|
|
}
|
|
highBit--
|
|
}
|
|
|
|
tagBytes := int(math.Ceil(float64(highBit) / 7.0))
|
|
for i := tagBytes - 1; i >= 0; i-- {
|
|
offset := uint(i) * 7
|
|
mask := Tag(0x7f) << offset
|
|
tagByte := (tag & mask) >> offset
|
|
if i != 0 {
|
|
tagByte |= 0x80
|
|
}
|
|
b = append(b, byte(tagByte))
|
|
}
|
|
}
|
|
return b
|
|
}
|