1 // Copyright 2008 Google Inc.
2 // Author: Lincoln Smith
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15
16 #include <config.h>
17 #include "varint_bigendian.h"
18 #include <stdint.h> // int32_t, int64_t
19 #include <string.h> // memcpy
20 #include <string>
21 #include "logging.h"
22 #include "google/output_string.h"
23
24 namespace open_vcdiff {
25
26 template<> const int32_t VarintBE<int32_t>::kMaxVal = 0x7FFFFFFF;
27 template<> const int64_t VarintBE<int64_t>::kMaxVal = 0x7FFFFFFFFFFFFFFFULL;
28
29 // Reads a variable-length integer from **varint_ptr
30 // and returns it in a fixed-length representation. Increments
31 // *varint_ptr by the number of bytes read. Will not read
32 // past limit. Returns RESULT_ERROR if the value parsed
33 // does not fit in a non-negative signed integer, or if limit is NULL.
34 // Returns RESULT_END_OF_DATA if address_stream_end is reached
35 // before the whole integer can be decoded.
36 //
37 template <typename SignedIntegerType>
Parse(const char * limit,const char ** varint_ptr)38 SignedIntegerType VarintBE<SignedIntegerType>::Parse(const char* limit,
39 const char** varint_ptr) {
40 if (!limit) {
41 return RESULT_ERROR;
42 }
43 SignedIntegerType result = 0;
44 for (const char* parse_ptr = *varint_ptr; parse_ptr < limit; ++parse_ptr) {
45 result += *parse_ptr & 0x7F;
46 if (!(*parse_ptr & 0x80)) {
47 *varint_ptr = parse_ptr + 1;
48 return result;
49 }
50 if (result > (kMaxVal >> 7)) {
51 // Shifting result by 7 bits would produce a number too large
52 // to be stored in a non-negative SignedIntegerType (an overflow.)
53 return RESULT_ERROR;
54 }
55 result = result << 7;
56 }
57 return RESULT_END_OF_DATA;
58 }
59
60 template <typename SignedIntegerType>
EncodeInternal(SignedIntegerType v,char * varint_buf)61 int VarintBE<SignedIntegerType>::EncodeInternal(SignedIntegerType v,
62 char* varint_buf) {
63 if (v < 0) {
64 LOG(DFATAL) << "Negative value " << v
65 << " passed to VarintBE::EncodeInternal,"
66 " which requires non-negative argument" << LOG_ENDL;
67 return 0;
68 }
69 int length = 1;
70 char* buf_ptr = &varint_buf[kMaxBytes - 1];
71 *buf_ptr = static_cast<char>(v & 0x7F);
72 --buf_ptr;
73 v >>= 7;
74 while (v) {
75 *buf_ptr = static_cast<char>((v & 0x7F) | 0x80); // add continuation bit
76 --buf_ptr;
77 ++length;
78 v >>= 7;
79 }
80 return length;
81 }
82
83 template <typename SignedIntegerType>
Encode(SignedIntegerType v,char * ptr)84 int VarintBE<SignedIntegerType>::Encode(SignedIntegerType v, char* ptr) {
85 char varint_buf[kMaxBytes];
86 const int length = EncodeInternal(v, varint_buf);
87 memcpy(ptr, &varint_buf[kMaxBytes - length], length);
88 return length;
89 }
90
91 template <typename SignedIntegerType>
AppendToString(SignedIntegerType value,string * s)92 void VarintBE<SignedIntegerType>::AppendToString(SignedIntegerType value,
93 string* s) {
94 char varint_buf[kMaxBytes];
95 const int length = EncodeInternal(value, varint_buf);
96 s->append(&varint_buf[kMaxBytes - length], length);
97 }
98
99 template <typename SignedIntegerType>
AppendToOutputString(SignedIntegerType value,OutputStringInterface * output_string)100 void VarintBE<SignedIntegerType>::AppendToOutputString(
101 SignedIntegerType value,
102 OutputStringInterface* output_string) {
103 char varint_buf[kMaxBytes];
104 const int length = EncodeInternal(value, varint_buf);
105 output_string->append(&varint_buf[kMaxBytes - length], length);
106 }
107
108 // Returns the encoding length of the specified value.
109 template <typename SignedIntegerType>
Length(SignedIntegerType v)110 int VarintBE<SignedIntegerType>::Length(SignedIntegerType v) {
111 if (v < 0) {
112 LOG(DFATAL) << "Negative value " << v
113 << " passed to VarintBE::Length,"
114 " which requires non-negative argument" << LOG_ENDL;
115 return 0;
116 }
117 int length = 0;
118 do {
119 v >>= 7;
120 ++length;
121 } while (v);
122 return length;
123 }
124
125 template class VarintBE<int32_t>;
126 template class VarintBE<int64_t>;
127
128 } // namespace open_vcdiff
129