xref: /aosp_15_r20/external/icing/icing/util/fingerprint-util.cc (revision 8b6cd535a057e39b3b86660c4aa06c99747c2136)
1 // Copyright (C) 2022 Google LLC
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //      http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #include "icing/util/fingerprint-util.h"
16 
17 namespace icing {
18 namespace lib {
19 
20 namespace fingerprint_util {
21 
22 // A formatter to properly handle a string that is actually just a hash value.
GetFingerprintString(uint64_t fingerprint)23 std::string GetFingerprintString(uint64_t fingerprint) {
24   std::string encoded_fprint;
25   // DynamicTrie cannot handle keys with '0' as bytes. So, we encode it in
26   // base128 and add 1 to make sure that no byte is '0'. This increases the
27   // size of the encoded_fprint from 8-bytes to 10-bytes.
28   while (fingerprint) {
29     encoded_fprint.push_back((fingerprint & 0x7F) + 1);
30     fingerprint >>= 7;
31   }
32   return encoded_fprint;
33 }
34 
GetFingerprint(std::string_view fingerprint_string)35 uint64_t GetFingerprint(std::string_view fingerprint_string) {
36   uint64_t fprint = 0;
37   for (int i = fingerprint_string.length() - 1; i >= 0; --i) {
38     fprint <<= 7;
39     char c = fingerprint_string[i] - 1;
40     fprint |= (c & 0x7F);
41   }
42   return fprint;
43 }
44 
45 }  // namespace fingerprint_util
46 
47 }  // namespace lib
48 }  // namespace icing
49