1//===- llvm/ADT/StableHashing.h - Utilities for stable hashing * C++ *-----===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file provides types and functions for computing and combining stable
10// hashes. Stable hashes can be useful for hashing across different modules,
11// processes, or compiler runs.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_STABLEHASHING_H
16#define LLVM_ADT_STABLEHASHING_H
17
18#include "llvm/ADT/StringRef.h"
19
20namespace llvm {
21
22/// An opaque object representing a stable hash code. It can be serialized,
23/// deserialized, and is stable across processes and executions.
24using stable_hash = uint64_t;
25
26// Implementation details
27namespace hashing {
28namespace detail {
29
30// Stable hashes are based on the 64-bit FNV-1 hash:
31// https://en.wikipedia.org/wiki/Fowler-Noll-Vo_hash_function
32
33const uint64_t FNV_PRIME_64 = 1099511628211u;
34const uint64_t FNV_OFFSET_64 = 14695981039346656037u;
35
36inline void stable_hash_append(stable_hash &Hash, const char Value) {
37 Hash = Hash ^ (Value & 0xFF);
38 Hash = Hash * FNV_PRIME_64;
39}
40
41inline void stable_hash_append(stable_hash &Hash, stable_hash Value) {
42 for (unsigned I = 0; I < 8; ++I) {
43 stable_hash_append(Hash, Value: static_cast<char>(Value));
44 Value >>= 8;
45 }
46}
47
48} // namespace detail
49} // namespace hashing
50
51inline stable_hash stable_hash_combine(stable_hash A, stable_hash B) {
52 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
53 hashing::detail::stable_hash_append(Hash, Value: A);
54 hashing::detail::stable_hash_append(Hash, Value: B);
55 return Hash;
56}
57
58inline stable_hash stable_hash_combine(stable_hash A, stable_hash B,
59 stable_hash C) {
60 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
61 hashing::detail::stable_hash_append(Hash, Value: A);
62 hashing::detail::stable_hash_append(Hash, Value: B);
63 hashing::detail::stable_hash_append(Hash, Value: C);
64 return Hash;
65}
66
67inline stable_hash stable_hash_combine(stable_hash A, stable_hash B,
68 stable_hash C, stable_hash D) {
69 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
70 hashing::detail::stable_hash_append(Hash, Value: A);
71 hashing::detail::stable_hash_append(Hash, Value: B);
72 hashing::detail::stable_hash_append(Hash, Value: C);
73 hashing::detail::stable_hash_append(Hash, Value: D);
74 return Hash;
75}
76
77/// Compute a stable_hash for a sequence of values.
78///
79/// This hashes a sequence of values. It produces the same stable_hash as
80/// 'stable_hash_combine(a, b, c, ...)', but can run over arbitrary sized
81/// sequences and is significantly faster given pointers and types which
82/// can be hashed as a sequence of bytes.
83template <typename InputIteratorT>
84stable_hash stable_hash_combine_range(InputIteratorT First,
85 InputIteratorT Last) {
86 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
87 for (auto I = First; I != Last; ++I)
88 hashing::detail::stable_hash_append(Hash, *I);
89 return Hash;
90}
91
92inline stable_hash stable_hash_combine_array(const stable_hash *P, size_t C) {
93 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
94 for (size_t I = 0; I < C; ++I)
95 hashing::detail::stable_hash_append(Hash, Value: P[I]);
96 return Hash;
97}
98
99inline stable_hash stable_hash_combine_string(const StringRef &S) {
100 return stable_hash_combine_range(First: S.begin(), Last: S.end());
101}
102
103inline stable_hash stable_hash_combine_string(const char *C) {
104 stable_hash Hash = hashing::detail::FNV_OFFSET_64;
105 while (*C)
106 hashing::detail::stable_hash_append(Hash, Value: *(C++));
107 return Hash;
108}
109
110} // namespace llvm
111
112#endif
113

source code of llvm/include/llvm/ADT/StableHashing.h