add SipHash.h from llvm-22.1.6 which is shipped as a third party header

gnu/llvm/siphash/include/siphash/SipHash.h

@@ -0,0 +1,160 @@
+//===--- SipHash.h - An implementation of SipHash -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+//  This is a header-only implementation of SipHash. It lacks library
+//  dependencies so it can be used from LLVM and compiler-rt.
+//
+//===----------------------------------------------------------------------===//
+
+#include <stddef.h>
+#include <stdint.h>
+
+// Lightly adapted from the SipHash reference C implementation:
+//   https://github.com/veorq/SipHash
+// by Jean-Philippe Aumasson and Daniel J. Bernstein
+
+#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) |                 \
+     ((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)
+
+namespace {
+
+/// Computes a SipHash value
+///
+/// \param in: pointer to input data (read-only)
+/// \param inlen: input data length in bytes (any size_t value)
+/// \param k: reference to the key data 16-byte array (read-only)
+/// \returns output data, must be 8 or 16 bytes
+///
+template <int cROUNDS, int dROUNDS, size_t outlen>
+void siphash(const unsigned char *in, uint64_t inlen,
+             const unsigned char (&k)[16], unsigned char (&out)[outlen]) {
+
+  const unsigned char *ni = (const unsigned char *)in;
+  const unsigned char *kk = (const unsigned char *)k;
+
+  static_assert(outlen == 8 || outlen == 16, "result should be 8 or 16 bytes");
+
+  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;
+
+    for (i = 0; i < cROUNDS; ++i)
+      SIPROUND;
+
+    v0 ^= m;
+  }
+
+  switch (left) {
+  case 7:
+    b |= ((uint64_t)ni[6]) << 48;
+    [[fallthrough]];
+  case 6:
+    b |= ((uint64_t)ni[5]) << 40;
+    [[fallthrough]];
+  case 5:
+    b |= ((uint64_t)ni[4]) << 32;
+    [[fallthrough]];
+  case 4:
+    b |= ((uint64_t)ni[3]) << 24;
+    [[fallthrough]];
+  case 3:
+    b |= ((uint64_t)ni[2]) << 16;
+    [[fallthrough]];
+  case 2:
+    b |= ((uint64_t)ni[1]) << 8;
+    [[fallthrough]];
+  case 1:
+    b |= ((uint64_t)ni[0]);
+    break;
+  case 0:
+    break;
+  }
+
+  v3 ^= b;
+
+  for (i = 0; i < cROUNDS; ++i)
+    SIPROUND;
+
+  v0 ^= b;
+
+  if (outlen == 16)
+    v2 ^= 0xee;
+  else
+    v2 ^= 0xff;
+
+  for (i = 0; i < dROUNDS; ++i)
+    SIPROUND;
+
+  b = v0 ^ v1 ^ v2 ^ v3;
+  U64TO8_LE(out, b);
+
+  if (outlen == 8)
+    return;
+
+  v1 ^= 0xdd;
+
+  for (i = 0; i < dROUNDS; ++i)
+    SIPROUND;
+
+  b = v0 ^ v1 ^ v2 ^ v3;
+  U64TO8_LE(out + 8, b);
+}
+
+} // end anonymous namespace