varint.go (1493B)
1 // Copyright 2017 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package catmsg 6 7 // This file implements varint encoding analogous to the one in encoding/binary. 8 // We need a string version of this function, so we add that here and then add 9 // the rest for consistency. 10 11 import "errors" 12 13 var ( 14 errIllegalVarint = errors.New("catmsg: illegal varint") 15 errVarintTooLarge = errors.New("catmsg: varint too large for uint64") 16 ) 17 18 const maxVarintBytes = 10 // maximum length of a varint 19 20 // encodeUint encodes x as a variable-sized integer into buf and returns the 21 // number of bytes written. buf must be at least maxVarintBytes long 22 func encodeUint(buf []byte, x uint64) (n int) { 23 for ; x > 127; n++ { 24 buf[n] = 0x80 | uint8(x&0x7F) 25 x >>= 7 26 } 27 buf[n] = uint8(x) 28 n++ 29 return n 30 } 31 32 func decodeUintString(s string) (x uint64, size int, err error) { 33 i := 0 34 for shift := uint(0); shift < 64; shift += 7 { 35 if i >= len(s) { 36 return 0, i, errIllegalVarint 37 } 38 b := uint64(s[i]) 39 i++ 40 x |= (b & 0x7F) << shift 41 if b&0x80 == 0 { 42 return x, i, nil 43 } 44 } 45 return 0, i, errVarintTooLarge 46 } 47 48 func decodeUint(b []byte) (x uint64, size int, err error) { 49 i := 0 50 for shift := uint(0); shift < 64; shift += 7 { 51 if i >= len(b) { 52 return 0, i, errIllegalVarint 53 } 54 c := uint64(b[i]) 55 i++ 56 x |= (c & 0x7F) << shift 57 if c&0x80 == 0 { 58 return x, i, nil 59 } 60 } 61 return 0, i, errVarintTooLarge 62 }