optimization: introduce `PresaltedSipHasher` for repeated hashing

diff --git a/src/crypto/siphash.cpp b/src/crypto/siphash.cpp
index 37ed9189..a6029716 100644
--- a/src/crypto/siphash.cpp
+++ b/src/crypto/siphash.cpp
@@ -137,17 +137,12 @@ uint64_t SipHashUint256(uint64_t k0, uint64_t k1, const uint256& val)
     return v0 ^ v1 ^ v2 ^ v3;
 }
 
-uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra)
+/** Specialized implementation for efficiency */
+uint64_t PresaltedSipHasher::operator()(const uint256& val, uint32_t extra) const noexcept
 {
-    /* Specialized implementation for efficiency */
+    uint64_t v0 = v[0], v1 = v[1], v2 = v[2], v3 = v[3];
     uint64_t d = val.GetUint64(0);
-
-    // TODO moved in followup commit
-    uint64_t v0 = CSipHasher::C0 ^ k0;
-    uint64_t v1 = CSipHasher::C1 ^ k1;
-    uint64_t v2 = CSipHasher::C2 ^ k0;
-    uint64_t v3 = CSipHasher::C3 ^ k1 ^ d;
-
+    v3 ^= d;
     SIPROUND;
     SIPROUND;
     v0 ^= d;
diff --git a/src/crypto/siphash.h b/src/crypto/siphash.h
index 4293fdf9..a4aeb3ae 100644
--- a/src/crypto/siphash.h
+++ b/src/crypto/siphash.h
@@ -48,6 +48,20 @@ public:
  *      .Finalize()
  */
 uint64_t SipHashUint256(uint64_t k0, uint64_t k1, const uint256& val);
-uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra);
+
+class PresaltedSipHasher
+{
+    uint64_t v[4];
+
+public:
+    explicit PresaltedSipHasher(uint64_t k0, uint64_t k1) noexcept {
+        v[0] = CSipHasher::C0 ^ k0;
+        v[1] = CSipHasher::C1 ^ k1;
+        v[2] = CSipHasher::C2 ^ k0;
+        v[3] = CSipHasher::C3 ^ k1;
+    }
+
+    uint64_t operator()(const uint256& val, uint32_t extra) const noexcept;
+};
 
 #endif // BITCOIN_CRYPTO_SIPHASH_H
diff --git a/src/test/fuzz/integer.cpp b/src/test/fuzz/integer.cpp
index 2e13d422..81516fd9 100644
--- a/src/test/fuzz/integer.cpp
+++ b/src/test/fuzz/integer.cpp
@@ -119,7 +119,7 @@ FUZZ_TARGET(integer, .init = initialize_integer)
     (void)MillisToTimeval(i64);
     (void)SighashToStr(uch);
     (void)SipHashUint256(u64, u64, u256);
-    (void)SipHashUint256Extra(u64, u64, u256, u32);
+    (void)PresaltedSipHasher(u64, u64)(u256, u32);
     (void)ToLower(ch);
     (void)ToUpper(ch);
     {
diff --git a/src/test/hash_tests.cpp b/src/test/hash_tests.cpp
index 46901893..d4592df7 100644
--- a/src/test/hash_tests.cpp
+++ b/src/test/hash_tests.cpp
@@ -130,7 +130,7 @@ BOOST_AUTO_TEST_CASE(siphash)
     ss << TX_WITH_WITNESS(tx);
     BOOST_CHECK_EQUAL(SipHashUint256(1, 2, ss.GetHash()), 0x79751e980c2a0a35ULL);
 
-    // Check consistency between CSipHasher and SipHashUint256[Extra].
+    // Check consistency between CSipHasher and SipHashUint256 and PresaltedSipHasher.
     FastRandomContext ctx;
     for (int i = 0; i < 16; ++i) {
         uint64_t k0 = ctx.rand64();
@@ -146,7 +146,7 @@ BOOST_AUTO_TEST_CASE(siphash)
         uint8_t nb[4];
         WriteLE32(nb, n);
         sip288.Write(nb);
-        BOOST_CHECK_EQUAL(SipHashUint256Extra(k0, k1, x, n), sip288.Finalize()); // TODO modified in follow-up commit
+        BOOST_CHECK_EQUAL(PresaltedSipHasher(k0, k1)(x, n), sip288.Finalize());
     }
 }
 
diff --git a/src/util/hasher.cpp b/src/util/hasher.cpp
index c4051ae0..cac602a8 100644
--- a/src/util/hasher.cpp
+++ b/src/util/hasher.cpp
@@ -19,14 +19,15 @@ SaltedWtxidHasher::SaltedWtxidHasher() :
     k0{FastRandomContext().rand64()},
     k1{FastRandomContext().rand64()} {}
 
-SaltedOutpointHasher::SaltedOutpointHasher(bool deterministic) :
-    k0{deterministic ? 0x8e819f2607a18de6 : FastRandomContext().rand64()},
-    k1{deterministic ? 0xf4020d2e3983b0eb : FastRandomContext().rand64()}
+SaltedOutpointHasher::SaltedOutpointHasher(bool deterministic) : m_hasher{
+    deterministic ? 0x8e819f2607a18de6 : FastRandomContext().rand64(),
+    deterministic ? 0xf4020d2e3983b0eb : FastRandomContext().rand64()}
 {}
 
 SaltedSipHasher::SaltedSipHasher() :
     m_k0{FastRandomContext().rand64()},
-    m_k1{FastRandomContext().rand64()} {}
+    m_k1{FastRandomContext().rand64()}
+{}
 
 size_t SaltedSipHasher::operator()(const std::span<const unsigned char>& script) const
 {
diff --git a/src/util/hasher.h b/src/util/hasher.h
index be5d9eb1..e7e69530 100644
--- a/src/util/hasher.h
+++ b/src/util/hasher.h
@@ -60,9 +60,7 @@ public:
 
 class SaltedOutpointHasher
 {
-private:
-    /** Salt */
-    const uint64_t k0, k1;
+    const PresaltedSipHasher m_hasher;
 
 public:
     SaltedOutpointHasher(bool deterministic = false);
@@ -76,8 +74,9 @@ public:
      *
      * @see https://gcc.gnu.org/onlinedocs/gcc-13.2.0/libstdc++/manual/manual/unordered_associative.html
      */
-    size_t operator()(const COutPoint& id) const noexcept {
-        return SipHashUint256Extra(k0, k1, id.hash.ToUint256(), id.n);
+    size_t operator()(const COutPoint& id) const noexcept
+    {
+        return m_hasher(id.hash.ToUint256(), id.n);
     }
 };