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memuvarint.go
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memuvarint.go
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// Copyright (c) 2020 The Bluge Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ice
import "fmt"
// ------------------------------------------------------------
type memUvarintReader struct {
C int // index of next byte to read from S
S []byte
}
func newMemUvarintReader(s []byte) *memUvarintReader {
return &memUvarintReader{S: s}
}
// Len returns the number of unread bytes.
func (r *memUvarintReader) Len() int {
n := len(r.S) - r.C
if n < 0 {
return 0
}
return n
}
// why 63? The original code had an 'i += 1' loop var and
// checked for i > 9 || i == 9 ...; but, we no longer
// check for the i var, but instead check here for s,
// which is incremented by 7. So, 7*9 == 63.
const sevenTimesNine = 63
// lastByte has the most significant bit set
// indicating there are more bytes in the stream
// any value less than this is a terminal byte
const lastByte = 0x80
// significantBits masks the significant bits
// the highest order bit is used to indicate
// the presence of more data
const significantBits = 0x7f
// ReadUvarint reads an encoded uint64. The original code this was
// based on is at encoding/binary/ReadUvarint().
func (r *memUvarintReader) ReadUvarint() (uint64, error) {
var x uint64
var s uint
var C = r.C
var S = r.S
for {
b := S[C]
C++
if b < lastByte {
r.C = C
// why the "extra" >= check? The normal case is that s <
// 63, so we check this single >= guard first so that we
// hit the normal, nil-error return pathway sooner.
if s >= sevenTimesNine && (s > sevenTimesNine || s == sevenTimesNine && b > 1) {
return 0, fmt.Errorf("memUvarintReader overflow")
}
return x | uint64(b)<<s, nil
}
x |= uint64(b&significantBits) << s
s += 7
}
}
// SkipUvarint skips ahead one encoded uint64.
func (r *memUvarintReader) SkipUvarint() {
for {
b := r.S[r.C]
r.C++
if b < lastByte {
return
}
}
}
// SkipBytes skips a count number of bytes.
func (r *memUvarintReader) SkipBytes(count int) {
r.C += count
}
func (r *memUvarintReader) Reset(s []byte) {
r.C = 0
r.S = s
}