Repository: bitcoin/bitcoin
File: src/script/sigcache.cpp (C++)

Code before:
#include <uint256.h>

#include <mutex>
#include <shared_mutex>
#include <vector>

SignatureCache::SignatureCache(const size_t max_size_bytes)
{
    uint256 nonce = GetRandHash();
    // We want the nonce to be 64 bytes long to force the hasher to process
    // this chunk, which makes later hash computations more efficient. We
    // just write our 32-byte entropy, and then pad with 'E' for ECDSA and
    // 'S' for Schnorr (followed by 0 bytes).
    static constexpr unsigned char PADDING_ECDSA[32] = {'E'};
    static constexpr unsigned char PADDING_SCHNORR[32] = {'S'};
    m_salted_hasher_ecdsa.Write(nonce.begin(), 32);
    m_salted_hasher_ecdsa.Write(PADDING_ECDSA, 32);
    m_salted_hasher_schnorr.Write(nonce.begin(), 32);
    m_salted_hasher_schnorr.Write(PADDING_SCHNORR, 32);

    const auto [num_elems, approx_size_bytes] = setValid.setup_bytes(max_size_bytes);
    LogPrintf("Using %zu MiB out of %zu MiB requested for signature cache, able to store %zu elements\n",
              approx_size_bytes >> 20, max_size_bytes >> 20, num_elems);
}

void SignatureCache::ComputeEntryECDSA(uint256& entry, const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey) const
{
    CSHA256 hasher = m_salted_hasher_ecdsa;
    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(vchSig.data(), vchSig.size()).Finalize(entry.begin());
}

void SignatureCache::ComputeEntrySchnorr(uint256& entry, const uint256 &hash, Span<const unsigned char> sig, const XOnlyPubKey& pubkey) const
{
    CSHA256 hasher = m_salted_hasher_schnorr;
    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(sig.data(), sig.size()).Finalize(entry.begin());
}

bool SignatureCache::Get(const uint256& entry, const bool erase)
{
    std::shared_lock<std::shared_mutex> lock(cs_sigcache);
    return setValid.contains(entry, erase);
}

void SignatureCache::Set(const uint256& entry)
{
    std::unique_lock<std::shared_mutex> lock(cs_sigcache);
    setValid.insert(entry);
}

bool CachingTransactionSignatureChecker::VerifyECDSASignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
{

Review comment (performance):
nit: since this line isn't a move-only change anyway, could address clang-tidy fix (+ for `SignatureCache::ComputeEntrySchnorr`)

```suggestion
void SignatureCache::ComputeEntryECDSA(uint256& entry, const uint256& hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey) const
```

Code after:
#include <uint256.h>

#include <mutex>
#include <shared_mutex>
#include <vector>

SignatureCache::SignatureCache(const size_t max_size_bytes)
{
    uint256 nonce = GetRandHash();
    // We want the nonce to be 64 bytes long to force the hasher to process
    // this chunk, which makes later hash computations more efficient. We
    // just write our 32-byte entropy, and then pad with 'E' for ECDSA and
    // 'S' for Schnorr (followed by 0 bytes).
    static constexpr unsigned char PADDING_ECDSA[32] = {'E'};
    static constexpr unsigned char PADDING_SCHNORR[32] = {'S'};
    m_salted_hasher_ecdsa.Write(nonce.begin(), 32);
    m_salted_hasher_ecdsa.Write(PADDING_ECDSA, 32);
    m_salted_hasher_schnorr.Write(nonce.begin(), 32);
    m_salted_hasher_schnorr.Write(PADDING_SCHNORR, 32);

    const auto [num_elems, approx_size_bytes] = setValid.setup_bytes(max_size_bytes);
    LogPrintf("Using %zu MiB out of %zu MiB requested for signature cache, able to store %zu elements\n",
              approx_size_bytes >> 20, max_size_bytes >> 20, num_elems);
}

void SignatureCache::ComputeEntryECDSA(uint256& entry, const uint256& hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubkey) const
{
    CSHA256 hasher = m_salted_hasher_ecdsa;
    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(vchSig.data(), vchSig.size()).Finalize(entry.begin());
}

void SignatureCache::ComputeEntrySchnorr(uint256& entry, const uint256& hash, Span<const unsigned char> sig, const XOnlyPubKey& pubkey) const
{
    CSHA256 hasher = m_salted_hasher_schnorr;
    hasher.Write(hash.begin(), 32).Write(pubkey.data(), pubkey.size()).Write(sig.data(), sig.size()).Finalize(entry.begin());
}

bool SignatureCache::Get(const uint256& entry, const bool erase)
{
    std::shared_lock<std::shared_mutex> lock(cs_sigcache);
    return setValid.contains(entry, erase);
}

void SignatureCache::Set(const uint256& entry)
{
    std::unique_lock<std::shared_mutex> lock(cs_sigcache);
    setValid.insert(entry);
}

bool CachingTransactionSignatureChecker::VerifyECDSASignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
{