[llvm-branch-commits] [llvm] [Support] Integrate SipHash.cpp into libSupport. (PR #94394)

Ahmed Bougacha via llvm-branch-commits llvm-branch-commits at lists.llvm.org
Tue Jun 4 13:05:29 PDT 2024


https://github.com/ahmedbougacha created https://github.com/llvm/llvm-project/pull/94394

Start building it as part of the library, with some minor
tweaks compared to the reference implementation:
- clang-format to match libSupport
- remove tracing support
- add file header
- templatize cROUNDS/dROUNDS, as well as 8B/16B result type
- replace assert with static_assert
- return the result directly, as uint64_t/uint128_t
- remove big-endian support
- use LLVM_FALLTHROUGH
- remove tracing support

The siphash function itself isn't used yet, and will be in a follow-up
commit.

>From 12bb6238aa0e7f90342aa194e54a8286e3e35dbd Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed at bougacha.org>
Date: Tue, 4 Jun 2024 12:41:47 -0700
Subject: [PATCH 1/3] [Support] Reformat SipHash.cpp to match libSupport.

While there, give it our usual file header and an acknowledgement,
and remove the imported README.md.SipHash.
---
 llvm/lib/Support/README.md.SipHash | 126 --------------
 llvm/lib/Support/SipHash.cpp       | 264 ++++++++++++++---------------
 2 files changed, 129 insertions(+), 261 deletions(-)
 delete mode 100644 llvm/lib/Support/README.md.SipHash

diff --git a/llvm/lib/Support/README.md.SipHash b/llvm/lib/Support/README.md.SipHash
deleted file mode 100644
index 4de3cd1854681..0000000000000
--- a/llvm/lib/Support/README.md.SipHash
+++ /dev/null
@@ -1,126 +0,0 @@
-# SipHash
-
-[![License:
-CC0-1.0](https://licensebuttons.net/l/zero/1.0/80x15.png)](http://creativecommons.org/publicdomain/zero/1.0/)
-
-[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
-
-
-SipHash is a family of pseudorandom functions (PRFs) optimized for speed on short messages.
-This is the reference C code of SipHash: portable, simple, optimized for clarity and debugging.
-
-SipHash was designed in 2012 by [Jean-Philippe Aumasson](https://aumasson.jp)
-and [Daniel J. Bernstein](https://cr.yp.to) as a defense against [hash-flooding
-DoS attacks](https://aumasson.jp/siphash/siphashdos_29c3_slides.pdf).
-
-SipHash is:
-
-* *Simpler and faster* on short messages than previous cryptographic
-algorithms, such as MACs based on universal hashing.
-
-* *Competitive in performance* with insecure non-cryptographic algorithms, such as [fhhash](https://github.com/cbreeden/fxhash).
-
-* *Cryptographically secure*, with no sign of weakness despite multiple [cryptanalysis](https://eprint.iacr.org/2019/865) [projects](https://eprint.iacr.org/2019/865) by leading cryptographers.
-
-* *Battle-tested*, with successful integration in OSs (Linux kernel, OpenBSD,
-FreeBSD, FreeRTOS), languages (Perl, Python, Ruby, etc.), libraries (OpenSSL libcrypto,
-Sodium, etc.) and applications (Wireguard, Redis, etc.).
-
-As a secure pseudorandom function (a.k.a. keyed hash function), SipHash can also be used as a secure message authentication code (MAC).
-But SipHash is *not a hash* in the sense of general-purpose key-less hash function such as BLAKE3 or SHA-3.
-SipHash should therefore always be used with a secret key in order to be secure.
-
-
-## Variants
-
-The default SipHash is *SipHash-2-4*: it takes a 128-bit key, does 2 compression
-rounds, 4 finalization rounds, and returns a 64-bit tag.
-
-Variants can use a different number of rounds. For example, we proposed *SipHash-4-8* as a conservative version.
-
-The following versions are not described in the paper but were designed and analyzed to fulfill applications' needs:
-
-* *SipHash-128* returns a 128-bit tag instead of 64-bit. Versions with specified number of rounds are SipHash-2-4-128, SipHash4-8-128, and so on.
-
-* *HalfSipHash* works with 32-bit words instead of 64-bit, takes a 64-bit key,
-and returns 32-bit or 64-bit tags. For example, HalfSipHash-2-4-32 has 2
-compression rounds, 4 finalization rounds, and returns a 32-bit tag.
-
-
-## Security
-
-(Half)SipHash-*c*-*d* with *c* ≥ 2 and *d* ≥ 4 is expected to provide the maximum PRF
-security for any function with the same key and output size.
-
-The standard PRF security goal allow the attacker access to the output of SipHash on messages chosen adaptively by the attacker.
-
-Security is limited by the key size (128 bits for SipHash), such that
-attackers searching 2<sup>*s*</sup> keys have chance 2<sup>*s*−128</sup> of finding
-the SipHash key. 
-Security is also limited by the output size. In particular, when
-SipHash is used as a MAC, an attacker who blindly tries 2<sup>*s*</sup> tags will
-succeed with probability 2<sup>*s*-*t*</sup>, if *t* is that tag's bit size.
-
-
-## Research
-
-* [Research paper](https://www.aumasson.jp/siphash/siphash.pdf) "SipHash: a fast short-input PRF" (accepted at INDOCRYPT 2012)
-* [Slides](https://cr.yp.to/talks/2012.12.12/slides.pdf) of the presentation of SipHash at INDOCRYPT 2012 (Bernstein)
-* [Slides](https://www.aumasson.jp/siphash/siphash_slides.pdf) of the presentation of SipHash at the DIAC workshop (Aumasson)
-
-
-## Usage
-
-Running
-
-```sh
-  make
-```
-
-will build tests for 
-
-* SipHash-2-4-64
-* SipHash-2-4-128
-* HalfSipHash-2-4-32
-* HalfSipHash-2-4-64
-
-
-```C
-  ./test
-```
-
-verifies 64 test vectors, and
-
-```C
-  ./debug
-```
-
-does the same and prints intermediate values.
-
-The code can be adapted to implement SipHash-*c*-*d*, the version of SipHash
-with *c* compression rounds and *d* finalization rounds, by defining `cROUNDS`
-or `dROUNDS` when compiling.  This can be done with `-D` command line arguments
-to many compilers such as below.
-
-```sh
-gcc -Wall --std=c99 -DcROUNDS=2 -DdROUNDS=4 siphash.c halfsiphash.c test.c -o test
-```
-
-The `makefile` also takes *c* and *d* rounds values as parameters.
-
-```sh
-make cROUNDS=2 dROUNDS=4
-``` 
-
-Obviously, if the number of rounds is modified then the test vectors
-won't verify.
-
-## Intellectual property
-
-This code is copyright (c) 2014-2023 Jean-Philippe Aumasson, Daniel J.
-Bernstein. It is multi-licensed under
-
-* [CC0](./LICENCE_CC0)
-* [MIT](./LICENSE_MIT).
-* [Apache 2.0 with LLVM exceptions](./LICENSE_A2LLVM).
-
diff --git a/llvm/lib/Support/SipHash.cpp b/llvm/lib/Support/SipHash.cpp
index c6d16e205521d..f31023740011f 100644
--- a/llvm/lib/Support/SipHash.cpp
+++ b/llvm/lib/Support/SipHash.cpp
@@ -1,25 +1,19 @@
-/*
-   SipHash reference C implementation
-
-   Copyright (c) 2012-2022 Jean-Philippe Aumasson
-   <jeanphilippe.aumasson at gmail.com>
-   Copyright (c) 2012-2014 Daniel J. Bernstein <djb at cr.yp.to>
-
-   To the extent possible under law, the author(s) have dedicated all copyright
-   and related and neighboring rights to this software to the public domain
-   worldwide. This software is distributed without any warranty.
-
-   You should have received a copy of the CC0 Public Domain Dedication along
-   with
-   this software. If not, see
-   <http://creativecommons.org/publicdomain/zero/1.0/>.
- */
+//===--- SipHash.cpp - An ABI-stable string hash --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
 
 #include "siphash.h"
 #include <assert.h>
 #include <stddef.h>
 #include <stdint.h>
 
+// Lightly adapted from the SipHash reference C implementation by
+// Jean-Philippe Aumasson and Daniel J. Bernstein.
+
 /* default: SipHash-2-4 */
 #ifndef cROUNDS
 #define cROUNDS 2
@@ -31,49 +25,49 @@
 #define ROTL(x, b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))
 
 #define U32TO8_LE(p, v)                                                        \
-    (p)[0] = (uint8_t)((v));                                                   \
-    (p)[1] = (uint8_t)((v) >> 8);                                              \
-    (p)[2] = (uint8_t)((v) >> 16);                                             \
-    (p)[3] = (uint8_t)((v) >> 24);
+  (p)[0] = (uint8_t)((v));                                                     \
+  (p)[1] = (uint8_t)((v) >> 8);                                                \
+  (p)[2] = (uint8_t)((v) >> 16);                                               \
+  (p)[3] = (uint8_t)((v) >> 24);
 
 #define U64TO8_LE(p, v)                                                        \
-    U32TO8_LE((p), (uint32_t)((v)));                                           \
-    U32TO8_LE((p) + 4, (uint32_t)((v) >> 32));
+  U32TO8_LE((p), (uint32_t)((v)));                                             \
+  U32TO8_LE((p) + 4, (uint32_t)((v) >> 32));
 
 #define U8TO64_LE(p)                                                           \
-    (((uint64_t)((p)[0])) | ((uint64_t)((p)[1]) << 8) |                        \
-     ((uint64_t)((p)[2]) << 16) | ((uint64_t)((p)[3]) << 24) |                 \
-     ((uint64_t)((p)[4]) << 32) | ((uint64_t)((p)[5]) << 40) |                 \
-     ((uint64_t)((p)[6]) << 48) | ((uint64_t)((p)[7]) << 56))
+  (((uint64_t)((p)[0])) | ((uint64_t)((p)[1]) << 8) |                          \
+   ((uint64_t)((p)[2]) << 16) | ((uint64_t)((p)[3]) << 24) |                   \
+   ((uint64_t)((p)[4]) << 32) | ((uint64_t)((p)[5]) << 40) |                   \
+   ((uint64_t)((p)[6]) << 48) | ((uint64_t)((p)[7]) << 56))
 
 #define SIPROUND                                                               \
-    do {                                                                       \
-        v0 += v1;                                                              \
-        v1 = ROTL(v1, 13);                                                     \
-        v1 ^= v0;                                                              \
-        v0 = ROTL(v0, 32);                                                     \
-        v2 += v3;                                                              \
-        v3 = ROTL(v3, 16);                                                     \
-        v3 ^= v2;                                                              \
-        v0 += v3;                                                              \
-        v3 = ROTL(v3, 21);                                                     \
-        v3 ^= v0;                                                              \
-        v2 += v1;                                                              \
-        v1 = ROTL(v1, 17);                                                     \
-        v1 ^= v2;                                                              \
-        v2 = ROTL(v2, 32);                                                     \
-    } while (0)
+  do {                                                                         \
+    v0 += v1;                                                                  \
+    v1 = ROTL(v1, 13);                                                         \
+    v1 ^= v0;                                                                  \
+    v0 = ROTL(v0, 32);                                                         \
+    v2 += v3;                                                                  \
+    v3 = ROTL(v3, 16);                                                         \
+    v3 ^= v2;                                                                  \
+    v0 += v3;                                                                  \
+    v3 = ROTL(v3, 21);                                                         \
+    v3 ^= v0;                                                                  \
+    v2 += v1;                                                                  \
+    v1 = ROTL(v1, 17);                                                         \
+    v1 ^= v2;                                                                  \
+    v2 = ROTL(v2, 32);                                                         \
+  } while (0)
 
 #ifdef DEBUG_SIPHASH
 #include <stdio.h>
 
 #define TRACE                                                                  \
-    do {                                                                       \
-        printf("(%3zu) v0 %016" PRIx64 "\n", inlen, v0);                       \
-        printf("(%3zu) v1 %016" PRIx64 "\n", inlen, v1);                       \
-        printf("(%3zu) v2 %016" PRIx64 "\n", inlen, v2);                       \
-        printf("(%3zu) v3 %016" PRIx64 "\n", inlen, v3);                       \
-    } while (0)
+  do {                                                                         \
+    printf("(%3zu) v0 %016" PRIx64 "\n", inlen, v0);                           \
+    printf("(%3zu) v1 %016" PRIx64 "\n", inlen, v1);                           \
+    printf("(%3zu) v2 %016" PRIx64 "\n", inlen, v2);                           \
+    printf("(%3zu) v3 %016" PRIx64 "\n", inlen, v3);                           \
+  } while (0)
 #else
 #define TRACE
 #endif
@@ -82,104 +76,104 @@
     Computes a SipHash value
     *in: pointer to input data (read-only)
     inlen: input data length in bytes (any size_t value)
-    *k: pointer to the key data (read-only), must be 16 bytes 
+    *k: pointer to the key data (read-only), must be 16 bytes
     *out: pointer to output data (write-only), outlen bytes must be allocated
     outlen: length of the output in bytes, must be 8 or 16
 */
 int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
             const size_t outlen) {
 
-    const unsigned char *ni = (const unsigned char *)in;
-    const unsigned char *kk = (const unsigned char *)k;
-
-    assert((outlen == 8) || (outlen == 16));
-    uint64_t v0 = UINT64_C(0x736f6d6570736575);
-    uint64_t v1 = UINT64_C(0x646f72616e646f6d);
-    uint64_t v2 = UINT64_C(0x6c7967656e657261);
-    uint64_t v3 = UINT64_C(0x7465646279746573);
-    uint64_t k0 = U8TO64_LE(kk);
-    uint64_t k1 = U8TO64_LE(kk + 8);
-    uint64_t m;
-    int i;
-    const unsigned char *end = ni + inlen - (inlen % sizeof(uint64_t));
-    const int left = inlen & 7;
-    uint64_t b = ((uint64_t)inlen) << 56;
-    v3 ^= k1;
-    v2 ^= k0;
-    v1 ^= k1;
-    v0 ^= k0;
-
-    if (outlen == 16)
-        v1 ^= 0xee;
-
-    for (; ni != end; ni += 8) {
-        m = U8TO64_LE(ni);
-        v3 ^= m;
-
-        TRACE;
-        for (i = 0; i < cROUNDS; ++i)
-            SIPROUND;
-
-        v0 ^= m;
-    }
-
-    switch (left) {
-    case 7:
-        b |= ((uint64_t)ni[6]) << 48;
-        /* FALLTHRU */
-    case 6:
-        b |= ((uint64_t)ni[5]) << 40;
-        /* FALLTHRU */
-    case 5:
-        b |= ((uint64_t)ni[4]) << 32;
-        /* FALLTHRU */
-    case 4:
-        b |= ((uint64_t)ni[3]) << 24;
-        /* FALLTHRU */
-    case 3:
-        b |= ((uint64_t)ni[2]) << 16;
-        /* FALLTHRU */
-    case 2:
-        b |= ((uint64_t)ni[1]) << 8;
-        /* FALLTHRU */
-    case 1:
-        b |= ((uint64_t)ni[0]);
-        break;
-    case 0:
-        break;
-    }
-
-    v3 ^= b;
+  const unsigned char *ni = (const unsigned char *)in;
+  const unsigned char *kk = (const unsigned char *)k;
+
+  assert((outlen == 8) || (outlen == 16));
+  uint64_t v0 = UINT64_C(0x736f6d6570736575);
+  uint64_t v1 = UINT64_C(0x646f72616e646f6d);
+  uint64_t v2 = UINT64_C(0x6c7967656e657261);
+  uint64_t v3 = UINT64_C(0x7465646279746573);
+  uint64_t k0 = U8TO64_LE(kk);
+  uint64_t k1 = U8TO64_LE(kk + 8);
+  uint64_t m;
+  int i;
+  const unsigned char *end = ni + inlen - (inlen % sizeof(uint64_t));
+  const int left = inlen & 7;
+  uint64_t b = ((uint64_t)inlen) << 56;
+  v3 ^= k1;
+  v2 ^= k0;
+  v1 ^= k1;
+  v0 ^= k0;
+
+  if (outlen == 16)
+    v1 ^= 0xee;
+
+  for (; ni != end; ni += 8) {
+    m = U8TO64_LE(ni);
+    v3 ^= m;
 
     TRACE;
     for (i = 0; i < cROUNDS; ++i)
-        SIPROUND;
-
-    v0 ^= b;
-
-    if (outlen == 16)
-        v2 ^= 0xee;
-    else
-        v2 ^= 0xff;
-
-    TRACE;
-    for (i = 0; i < dROUNDS; ++i)
-        SIPROUND;
-
-    b = v0 ^ v1 ^ v2 ^ v3;
-    U64TO8_LE(out, b);
-
-    if (outlen == 8)
-        return 0;
+      SIPROUND;
+
+    v0 ^= m;
+  }
+
+  switch (left) {
+  case 7:
+    b |= ((uint64_t)ni[6]) << 48;
+    /* FALLTHRU */
+  case 6:
+    b |= ((uint64_t)ni[5]) << 40;
+    /* FALLTHRU */
+  case 5:
+    b |= ((uint64_t)ni[4]) << 32;
+    /* FALLTHRU */
+  case 4:
+    b |= ((uint64_t)ni[3]) << 24;
+    /* FALLTHRU */
+  case 3:
+    b |= ((uint64_t)ni[2]) << 16;
+    /* FALLTHRU */
+  case 2:
+    b |= ((uint64_t)ni[1]) << 8;
+    /* FALLTHRU */
+  case 1:
+    b |= ((uint64_t)ni[0]);
+    break;
+  case 0:
+    break;
+  }
+
+  v3 ^= b;
+
+  TRACE;
+  for (i = 0; i < cROUNDS; ++i)
+    SIPROUND;
+
+  v0 ^= b;
+
+  if (outlen == 16)
+    v2 ^= 0xee;
+  else
+    v2 ^= 0xff;
+
+  TRACE;
+  for (i = 0; i < dROUNDS; ++i)
+    SIPROUND;
+
+  b = v0 ^ v1 ^ v2 ^ v3;
+  U64TO8_LE(out, b);
+
+  if (outlen == 8)
+    return 0;
 
-    v1 ^= 0xdd;
+  v1 ^= 0xdd;
 
-    TRACE;
-    for (i = 0; i < dROUNDS; ++i)
-        SIPROUND;
+  TRACE;
+  for (i = 0; i < dROUNDS; ++i)
+    SIPROUND;
 
-    b = v0 ^ v1 ^ v2 ^ v3;
-    U64TO8_LE(out + 8, b);
+  b = v0 ^ v1 ^ v2 ^ v3;
+  U64TO8_LE(out + 8, b);
 
-    return 0;
+  return 0;
 }

>From a1dbd8a893cf6dfedf9342fbaf07c6661c0a03a0 Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed at bougacha.org>
Date: Tue, 4 Jun 2024 12:45:37 -0700
Subject: [PATCH 2/3] [Support] Remove SipHash tracing support.

---
 llvm/lib/Support/SipHash.cpp | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/llvm/lib/Support/SipHash.cpp b/llvm/lib/Support/SipHash.cpp
index f31023740011f..b7cc692b7d6b4 100644
--- a/llvm/lib/Support/SipHash.cpp
+++ b/llvm/lib/Support/SipHash.cpp
@@ -58,20 +58,6 @@
     v2 = ROTL(v2, 32);                                                         \
   } while (0)
 
-#ifdef DEBUG_SIPHASH
-#include <stdio.h>
-
-#define TRACE                                                                  \
-  do {                                                                         \
-    printf("(%3zu) v0 %016" PRIx64 "\n", inlen, v0);                           \
-    printf("(%3zu) v1 %016" PRIx64 "\n", inlen, v1);                           \
-    printf("(%3zu) v2 %016" PRIx64 "\n", inlen, v2);                           \
-    printf("(%3zu) v3 %016" PRIx64 "\n", inlen, v3);                           \
-  } while (0)
-#else
-#define TRACE
-#endif
-
 /*
     Computes a SipHash value
     *in: pointer to input data (read-only)
@@ -110,7 +96,6 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
     m = U8TO64_LE(ni);
     v3 ^= m;
 
-    TRACE;
     for (i = 0; i < cROUNDS; ++i)
       SIPROUND;
 
@@ -145,7 +130,6 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
 
   v3 ^= b;
 
-  TRACE;
   for (i = 0; i < cROUNDS; ++i)
     SIPROUND;
 
@@ -156,7 +140,6 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
   else
     v2 ^= 0xff;
 
-  TRACE;
   for (i = 0; i < dROUNDS; ++i)
     SIPROUND;
 
@@ -168,7 +151,6 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
 
   v1 ^= 0xdd;
 
-  TRACE;
   for (i = 0; i < dROUNDS; ++i)
     SIPROUND;
 

>From 1d8561032aeb0df7030b5a69267410ecd58dd2fe Mon Sep 17 00:00:00 2001
From: Ahmed Bougacha <ahmed at bougacha.org>
Date: Tue, 4 Jun 2024 12:48:11 -0700
Subject: [PATCH 3/3] [Support] Integrate SipHash.cpp into libSupport.

Start building it as part of the library, with some minor
tweaks compared to the reference implementation:
- templatize cROUNDS/dROUNDS, as well as 8B/16B result type
- replace assert with static_assert
- return the result directly, as uint64_t/uint128_t
- remove big-endian support
- use LLVM_FALLTHROUGH

The siphash function itself isn't used yet, and will be in a follow-up
commit.
---
 llvm/lib/Support/CMakeLists.txt |  4 +-
 llvm/lib/Support/SipHash.cpp    | 67 +++++++++++----------------------
 2 files changed, 22 insertions(+), 49 deletions(-)

diff --git a/llvm/lib/Support/CMakeLists.txt b/llvm/lib/Support/CMakeLists.txt
index 7cc01a5399911..f5f8447d48d01 100644
--- a/llvm/lib/Support/CMakeLists.txt
+++ b/llvm/lib/Support/CMakeLists.txt
@@ -127,9 +127,6 @@ endif()
 
 add_subdirectory(BLAKE3)
 
-# Temporarily ignore SipHash.cpp before we fully integrate it into LLVMSupport.
-set(LLVM_OPTIONAL_SOURCES SipHash.cpp)
-
 add_llvm_component_library(LLVMSupport
   ABIBreak.cpp
   AMDGPUMetadata.cpp
@@ -226,6 +223,7 @@ add_llvm_component_library(LLVMSupport
   SHA1.cpp
   SHA256.cpp
   Signposts.cpp
+  SipHash.cpp
   SmallPtrSet.cpp
   SmallVector.cpp
   SourceMgr.cpp
diff --git a/llvm/lib/Support/SipHash.cpp b/llvm/lib/Support/SipHash.cpp
index b7cc692b7d6b4..8177b5359e8ed 100644
--- a/llvm/lib/Support/SipHash.cpp
+++ b/llvm/lib/Support/SipHash.cpp
@@ -6,34 +6,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "siphash.h"
-#include <assert.h>
-#include <stddef.h>
-#include <stdint.h>
+#include "llvm/Support/Compiler.h"
+#include <cstdint>
+#include <cstring>
 
 // Lightly adapted from the SipHash reference C implementation by
 // Jean-Philippe Aumasson and Daniel J. Bernstein.
 
-/* default: SipHash-2-4 */
-#ifndef cROUNDS
-#define cROUNDS 2
-#endif
-#ifndef dROUNDS
-#define dROUNDS 4
-#endif
-
 #define ROTL(x, b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))
 
-#define U32TO8_LE(p, v)                                                        \
-  (p)[0] = (uint8_t)((v));                                                     \
-  (p)[1] = (uint8_t)((v) >> 8);                                                \
-  (p)[2] = (uint8_t)((v) >> 16);                                               \
-  (p)[3] = (uint8_t)((v) >> 24);
-
-#define U64TO8_LE(p, v)                                                        \
-  U32TO8_LE((p), (uint32_t)((v)));                                             \
-  U32TO8_LE((p) + 4, (uint32_t)((v) >> 32));
-
 #define U8TO64_LE(p)                                                           \
   (((uint64_t)((p)[0])) | ((uint64_t)((p)[1]) << 8) |                          \
    ((uint64_t)((p)[2]) << 16) | ((uint64_t)((p)[3]) << 24) |                   \
@@ -58,21 +39,15 @@
     v2 = ROTL(v2, 32);                                                         \
   } while (0)
 
-/*
-    Computes a SipHash value
-    *in: pointer to input data (read-only)
-    inlen: input data length in bytes (any size_t value)
-    *k: pointer to the key data (read-only), must be 16 bytes
-    *out: pointer to output data (write-only), outlen bytes must be allocated
-    outlen: length of the output in bytes, must be 8 or 16
-*/
-int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
-            const size_t outlen) {
+template <int cROUNDS, int dROUNDS, class ResultTy>
+static inline ResultTy siphash(const unsigned char *in, uint64_t inlen,
+                               const unsigned char (&k)[16]) {
 
   const unsigned char *ni = (const unsigned char *)in;
   const unsigned char *kk = (const unsigned char *)k;
 
-  assert((outlen == 8) || (outlen == 16));
+  static_assert(sizeof(ResultTy) == 8 || sizeof(ResultTy) == 16,
+                "result type should be uint64_t or uint128_t");
   uint64_t v0 = UINT64_C(0x736f6d6570736575);
   uint64_t v1 = UINT64_C(0x646f72616e646f6d);
   uint64_t v2 = UINT64_C(0x6c7967656e657261);
@@ -89,7 +64,7 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
   v1 ^= k1;
   v0 ^= k0;
 
-  if (outlen == 16)
+  if (sizeof(ResultTy) == 16)
     v1 ^= 0xee;
 
   for (; ni != end; ni += 8) {
@@ -105,22 +80,22 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
   switch (left) {
   case 7:
     b |= ((uint64_t)ni[6]) << 48;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 6:
     b |= ((uint64_t)ni[5]) << 40;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 5:
     b |= ((uint64_t)ni[4]) << 32;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 4:
     b |= ((uint64_t)ni[3]) << 24;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 3:
     b |= ((uint64_t)ni[2]) << 16;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 2:
     b |= ((uint64_t)ni[1]) << 8;
-    /* FALLTHRU */
+    LLVM_FALLTHROUGH;
   case 1:
     b |= ((uint64_t)ni[0]);
     break;
@@ -135,7 +110,7 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
 
   v0 ^= b;
 
-  if (outlen == 16)
+  if (sizeof(ResultTy) == 16)
     v2 ^= 0xee;
   else
     v2 ^= 0xff;
@@ -144,10 +119,10 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
     SIPROUND;
 
   b = v0 ^ v1 ^ v2 ^ v3;
-  U64TO8_LE(out, b);
 
-  if (outlen == 8)
-    return 0;
+  uint64_t firstHalf = b;
+  if (sizeof(ResultTy) == 8)
+    return firstHalf;
 
   v1 ^= 0xdd;
 
@@ -155,7 +130,7 @@ int siphash(const void *in, const size_t inlen, const void *k, uint8_t *out,
     SIPROUND;
 
   b = v0 ^ v1 ^ v2 ^ v3;
-  U64TO8_LE(out + 8, b);
+  uint64_t secondHalf = b;
 
-  return 0;
+  return firstHalf | (ResultTy(secondHalf) << (sizeof(ResultTy) == 8 ? 0 : 64));
 }



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