1 //===-- Support/DJB.cpp ---DJB Hash -----------------------------*- 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 contains support for the DJ Bernstein hash function. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/Support/DJB.h" 14 #include "llvm/ADT/ArrayRef.h" 15 #include "llvm/Support/Compiler.h" 16 #include "llvm/Support/ConvertUTF.h" 17 #include "llvm/Support/Unicode.h" 18 19 using namespace llvm; 20 21 static UTF32 chopOneUTF32(StringRef &Buffer) { 22 UTF32 C; 23 const UTF8 *const Begin8Const = 24 reinterpret_cast<const UTF8 *>(Buffer.begin()); 25 const UTF8 *Begin8 = Begin8Const; 26 UTF32 *Begin32 = &C; 27 28 // In lenient mode we will always end up with a "reasonable" value in C for 29 // non-empty input. 30 assert(!Buffer.empty()); 31 ConvertUTF8toUTF32(&Begin8, reinterpret_cast<const UTF8 *>(Buffer.end()), 32 &Begin32, &C + 1, lenientConversion); 33 Buffer = Buffer.drop_front(Begin8 - Begin8Const); 34 return C; 35 } 36 37 static StringRef toUTF8(UTF32 C, MutableArrayRef<UTF8> Storage) { 38 const UTF32 *Begin32 = &C; 39 UTF8 *Begin8 = Storage.begin(); 40 41 // The case-folded output should always be a valid unicode character, so use 42 // strict mode here. 43 ConversionResult CR = ConvertUTF32toUTF8(&Begin32, &C + 1, &Begin8, 44 Storage.end(), strictConversion); 45 assert(CR == conversionOK && "Case folding produced invalid char?"); 46 (void)CR; 47 return StringRef(reinterpret_cast<char *>(Storage.begin()), 48 Begin8 - Storage.begin()); 49 } 50 51 static UTF32 foldCharDwarf(UTF32 C) { 52 // DWARF v5 addition to the unicode folding rules. 53 // Fold "Latin Small Letter Dotless I" and "Latin Capital Letter I With Dot 54 // Above" into "i". 55 if (C == 0x130 || C == 0x131) 56 return 'i'; 57 return sys::unicode::foldCharSimple(C); 58 } 59 60 static Optional<uint32_t> fastCaseFoldingDjbHash(StringRef Buffer, uint32_t H) { 61 bool AllASCII = true; 62 for (unsigned char C : Buffer) { 63 H = H * 33 + ('A' <= C && C <= 'Z' ? C - 'A' + 'a' : C); 64 AllASCII &= C <= 0x7f; 65 } 66 if (AllASCII) 67 return H; 68 return None; 69 } 70 71 uint32_t llvm::caseFoldingDjbHash(StringRef Buffer, uint32_t H) { 72 if (Optional<uint32_t> Result = fastCaseFoldingDjbHash(Buffer, H)) 73 return *Result; 74 75 std::array<UTF8, UNI_MAX_UTF8_BYTES_PER_CODE_POINT> Storage; 76 while (!Buffer.empty()) { 77 UTF32 C = foldCharDwarf(chopOneUTF32(Buffer)); 78 StringRef Folded = toUTF8(C, Storage); 79 H = djbHash(Folded, H); 80 } 81 return H; 82 } 83