[PATCH] D61178: caseFoldingDjbHash: simplify and make the US-ASCII fast path faster
Fangrui Song via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 26 03:42:21 PDT 2019
MaskRay updated this revision to Diff 196827.
MaskRay added a comment.
split into two functions
Repository:
rL LLVM
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D61178/new/
https://reviews.llvm.org/D61178
Files:
lib/Support/DJB.cpp
Index: lib/Support/DJB.cpp
===================================================================
--- lib/Support/DJB.cpp
+++ lib/Support/DJB.cpp
@@ -57,29 +57,26 @@
return sys::unicode::foldCharSimple(C);
}
-static uint32_t caseFoldingDjbHashCharSlow(StringRef &Buffer, uint32_t H) {
- UTF32 C = chopOneUTF32(Buffer);
-
- C = foldCharDwarf(C);
-
- std::array<UTF8, UNI_MAX_UTF8_BYTES_PER_CODE_POINT> Storage;
- StringRef Folded = toUTF8(C, Storage);
- return djbHash(Folded, H);
+static Optional<uint32_t> fastCaseFoldingDjbHash(StringRef Buffer, uint32_t H) {
+ bool allASCII = true;
+ for (unsigned char C : Buffer) {
+ H = H * 33 + ('A' <= C && C <= 'Z' ? C - 'A' + 'a' : C);
+ allASCII &= C <= 0x7f;
+ }
+ if (allASCII)
+ return H;
+ return None;
}
uint32_t llvm::caseFoldingDjbHash(StringRef Buffer, uint32_t H) {
+ if (Optional<uint32_t> Result = fastCaseFoldingDjbHash(Buffer, H))
+ return *Result;
+
+ std::array<UTF8, UNI_MAX_UTF8_BYTES_PER_CODE_POINT> Storage;
while (!Buffer.empty()) {
- unsigned char C = Buffer.front();
- if (LLVM_LIKELY(C <= 0x7f)) {
- // US-ASCII, encoded as one character in utf-8.
- // This is by far the most common case, so handle this specially.
- if (C >= 'A' && C <= 'Z')
- C = 'a' + (C - 'A'); // fold uppercase into lowercase
- H = (H << 5) + H + C;
- Buffer = Buffer.drop_front();
- continue;
- }
- H = caseFoldingDjbHashCharSlow(Buffer, H);
+ UTF32 C = foldCharDwarf(chopOneUTF32(Buffer));
+ StringRef Folded = toUTF8(C, Storage);
+ H = djbHash(Folded, H);
}
return H;
}
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