1 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file. See the AUTHORS file for names of contributors.
4 //
5 // Endian-neutral encoding:
6 // * Fixed-length numbers are encoded with least-significant byte first
7 // * In addition we support variable length "varint" encoding
8 // * Strings are encoded prefixed by their length in varint format
9
10 #ifndef STORAGE_LEVELDB_UTIL_CODING_H_
11 #define STORAGE_LEVELDB_UTIL_CODING_H_
12
13 #include <stdint.h>
14 #include <string.h>
15 #include <string>
16 #include "leveldb/slice.h"
17 #include "port/port.h"
18
19 namespace leveldb {
20
21 // Standard Put... routines append to a string
22 extern void PutFixed32(std::string* dst, uint32_t value);
23 extern void PutFixed64(std::string* dst, uint64_t value);
24 extern void PutVarint32(std::string* dst, uint32_t value);
25 extern void PutVarint64(std::string* dst, uint64_t value);
26 extern void PutLengthPrefixedSlice(std::string* dst, const Slice& value);
27
28 // Standard Get... routines parse a value from the beginning of a Slice
29 // and advance the slice past the parsed value.
30 extern bool GetVarint32(Slice* input, uint32_t* value);
31 extern bool GetVarint64(Slice* input, uint64_t* value);
32 extern bool GetLengthPrefixedSlice(Slice* input, Slice* result);
33
34 // Pointer-based variants of GetVarint... These either store a value
35 // in *v and return a pointer just past the parsed value, or return
36 // NULL on error. These routines only look at bytes in the range
37 // [p..limit-1]
38 extern const char* GetVarint32Ptr(const char* p,const char* limit, uint32_t* v);
39 extern const char* GetVarint64Ptr(const char* p,const char* limit, uint64_t* v);
40
41 // Returns the length of the varint32 or varint64 encoding of "v"
42 extern int VarintLength(uint64_t v);
43
44 // Lower-level versions of Put... that write directly into a character buffer
45 // REQUIRES: dst has enough space for the value being written
46 extern void EncodeFixed32(char* dst, uint32_t value);
47 extern void EncodeFixed64(char* dst, uint64_t value);
48
49 // Lower-level versions of Put... that write directly into a character buffer
50 // and return a pointer just past the last byte written.
51 // REQUIRES: dst has enough space for the value being written
52 extern char* EncodeVarint32(char* dst, uint32_t value);
53 extern char* EncodeVarint64(char* dst, uint64_t value);
54
55 // Lower-level versions of Get... that read directly from a character buffer
56 // without any bounds checking.
57
DecodeFixed32(const char * ptr)58 inline uint32_t DecodeFixed32(const char* ptr) {
59 if (port::kLittleEndian) {
60 // Load the raw bytes
61 uint32_t result;
62 memcpy(&result, ptr, sizeof(result)); // gcc optimizes this to a plain load
63 return result;
64 } else {
65 return ((static_cast<uint32_t>(static_cast<unsigned char>(ptr[0])))
66 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[1])) << 8)
67 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[2])) << 16)
68 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[3])) << 24));
69 }
70 }
71
DecodeFixed64(const char * ptr)72 inline uint64_t DecodeFixed64(const char* ptr) {
73 if (port::kLittleEndian) {
74 // Load the raw bytes
75 uint64_t result;
76 memcpy(&result, ptr, sizeof(result)); // gcc optimizes this to a plain load
77 return result;
78 } else {
79 uint64_t lo = DecodeFixed32(ptr);
80 uint64_t hi = DecodeFixed32(ptr + 4);
81 return (hi << 32) | lo;
82 }
83 }
84
85 // Internal routine for use by fallback path of GetVarint32Ptr
86 extern const char* GetVarint32PtrFallback(const char* p,
87 const char* limit,
88 uint32_t* value);
GetVarint32Ptr(const char * p,const char * limit,uint32_t * value)89 inline const char* GetVarint32Ptr(const char* p,
90 const char* limit,
91 uint32_t* value) {
92 if (p < limit) {
93 uint32_t result = *(reinterpret_cast<const unsigned char*>(p));
94 if ((result & 128) == 0) {
95 *value = result;
96 return p + 1;
97 }
98 }
99 return GetVarint32PtrFallback(p, limit, value);
100 }
101
102 } // namespace leveldb
103
104 #endif // STORAGE_LEVELDB_UTIL_CODING_H_
105