llvm/Support/SipHash.h

0001 //===--- SipHash.h - An ABI-stable string SipHash ---------------*- C++ -*-===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008 //
0009 // An implementation of SipHash, a hash function optimized for speed on
0010 // short inputs. Based on the SipHash reference implementation.
0011 //
0012 // Also provides one specific wrapper on top of SipHash-2-4-64 to compute
0013 // compute ABI-stable ptrauth discriminators.
0014 //
0015 //===----------------------------------------------------------------------===//
0016
0017 #ifndef LLVM_SUPPORT_SIPHASH_H
0018 #define LLVM_SUPPORT_SIPHASH_H
0019
0020 #include <cstdint>
0021
0022 namespace llvm {
0023
0024 template <typename T> class ArrayRef;
0025 class StringRef;
0026
0027 /// Computes a SipHash-2-4 64-bit result.
0028 void getSipHash_2_4_64(ArrayRef<uint8_t> In, const uint8_t (&K)[16],
0029                        uint8_t (&Out)[8]);
0030
0031 /// Computes a SipHash-2-4 128-bit result.
0032 void getSipHash_2_4_128(ArrayRef<uint8_t> In, const uint8_t (&K)[16],
0033                         uint8_t (&Out)[16]);
0034
0035 /// Compute a stable non-zero 16-bit hash of the given string.
0036 ///
0037 /// The exact algorithm is the little-endian interpretation of the
0038 /// non-doubled (i.e. 64-bit) result of applying a SipHash-2-4 using
0039 /// a specific seed value which can be found in the source.
0040 /// This 64-bit result is truncated to a non-zero 16-bit value.
0041 ///
0042 /// We use a 16-bit discriminator because ARM64 can efficiently load
0043 /// a 16-bit immediate into the high bits of a register without disturbing
0044 /// the remainder of the value, which serves as a nice blend operation.
0045 /// 16 bits is also sufficiently compact to not inflate a loader relocation.
0046 /// We disallow zero to guarantee a different discriminator from the places
0047 /// in the ABI that use a constant zero.
0048 uint16_t getPointerAuthStableSipHash(StringRef S);
0049
0050 } // end namespace llvm
0051
0052 #endif