Merge #10192: Cache full script execution results in addition to signatures

laanwj · laanwj · commit 2935b469ae96 · 2017-06-29T20:19:21.000+02:00
e3f9c05 Add CheckInputs() unit tests (Suhas Daftuar) a3543af Better document CheckInputs parameter meanings (Matt Corallo) 309ee1a Update -maxsigcachesize doc clarify init logprints for it (Matt Corallo) b014668 Add CheckInputs wrapper CCoinsViewMemPool -> non-consensus-critical (Matt Corallo) eada04e Do not print soft-fork-script warning with -promiscuousmempool (Matt Corallo) b5fea8d Cache full script execution results in addition to signatures (Matt Corallo) 6d22b2b Pull script verify flags calculation out of ConnectBlock (Matt Corallo) Tree-SHA512: 0c6c3c79c64fcb21e17ab60290c5c96d4fac11624c49f841a4201eec21cb480314c52a07d1e3abd4f9c764785cc57bfd178511f495aa0469addb204e96214fe4
diff --git a/src/init.cpp b/src/init.cpp
@@ -447,7 +447,7 @@ std::string HelpMessage(HelpMessageMode mode)
     {
         strUsage += HelpMessageOpt("-logtimemicros", strprintf("Add microsecond precision to debug timestamps (default: %u)", DEFAULT_LOGTIMEMICROS));
         strUsage += HelpMessageOpt("-mocktime=<n>", "Replace actual time with <n> seconds since epoch (default: 0)");
-        strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit size of signature cache to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));
+        strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit sum of signature cache and script execution cache sizes to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));
         strUsage += HelpMessageOpt("-maxtipage=<n>", strprintf("Maximum tip age in seconds to consider node in initial block download (default: %u)", DEFAULT_MAX_TIP_AGE));
     }
     strUsage += HelpMessageOpt("-maxtxfee=<amt>", strprintf(_("Maximum total fees (in %s) to use in a single wallet transaction or raw transaction; setting this too low may abort large transactions (default: %s)"),
@@ -1191,6 +1191,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
     LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);
 
     InitSignatureCache();
+    InitScriptExecutionCache();
 
     LogPrintf("Using %u threads for script verification\n", nScriptCheckThreads);
     if (nScriptCheckThreads) {
diff --git a/src/script/sigcache.cpp b/src/script/sigcache.cpp
@@ -74,10 +74,10 @@ void InitSignatureCache()
 {
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
-    size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE)), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+    size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
     size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);
-    LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",
-            (nElems*sizeof(uint256)) >>20, nMaxCacheSize>>20, nElems);
+    LogPrintf("Using %zu MiB out of %zu/2 requested for signature cache, able to store %zu elements\n",
+            (nElems*sizeof(uint256)) >>20, (nMaxCacheSize*2)>>20, nElems);
 }
 
 bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
@@ -38,6 +38,7 @@ BasicTestingSetup::BasicTestingSetup(const std::string& chainName)
         SetupEnvironment();
         SetupNetworking();
         InitSignatureCache();
+        InitScriptExecutionCache();
         fPrintToDebugLog = false; // don't want to write to debug.log file
         fCheckBlockIndex = true;
         SelectParams(chainName);
diff --git a/src/test/txvalidationcache_tests.cpp b/src/test/txvalidationcache_tests.cpp
@@ -10,11 +10,17 @@
 #include "txmempool.h"
 #include "random.h"
 #include "script/standard.h"
+#include "script/sign.h"
 #include "test/test_bitcoin.h"
 #include "utiltime.h"
+#include "core_io.h"
+#include "keystore.h"
+#include "policy/policy.h"
 
 #include <boost/test/unit_test.hpp>
 
+bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsViewCache &inputs, bool fScriptChecks, unsigned int flags, bool cacheSigStore, bool cacheFullScriptStore, PrecomputedTransactionData& txdata, std::vector<CScriptCheck> *pvChecks);
+
 BOOST_AUTO_TEST_SUITE(tx_validationcache_tests)
 
 static bool
@@ -84,4 +90,282 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_block_doublespend, TestChain100Setup)
     BOOST_CHECK_EQUAL(mempool.size(), 0);
 }
 
+// Run CheckInputs (using pcoinsTip) on the given transaction, for all script
+// flags.  Test that CheckInputs passes for all flags that don't overlap with
+// the failing_flags argument, but otherwise fails.
+// CHECKLOCKTIMEVERIFY and CHECKSEQUENCEVERIFY (and future NOP codes that may
+// get reassigned) have an interaction with DISCOURAGE_UPGRADABLE_NOPS: if
+// the script flags used contain DISCOURAGE_UPGRADABLE_NOPS but don't contain
+// CHECKLOCKTIMEVERIFY (or CHECKSEQUENCEVERIFY), but the script does contain
+// OP_CHECKLOCKTIMEVERIFY (or OP_CHECKSEQUENCEVERIFY), then script execution
+// should fail.
+// Capture this interaction with the upgraded_nop argument: set it when evaluating
+// any script flag that is implemented as an upgraded NOP code.
+void ValidateCheckInputsForAllFlags(CMutableTransaction &tx, uint32_t failing_flags, bool add_to_cache, bool upgraded_nop)
+{
+    PrecomputedTransactionData txdata(tx);
+    // If we add many more flags, this loop can get too expensive, but we can
+    // rewrite in the future to randomly pick a set of flags to evaluate.
+    for (uint32_t test_flags=0; test_flags < (1U << 16); test_flags += 1) {
+        CValidationState state;
+        // Filter out incompatible flag choices
+        if ((test_flags & SCRIPT_VERIFY_CLEANSTACK)) {
+            // CLEANSTACK requires P2SH and WITNESS, see VerifyScript() in
+            // script/interpreter.cpp
+            test_flags |= SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS;
+        }
+        if ((test_flags & SCRIPT_VERIFY_WITNESS)) {
+            // WITNESS requires P2SH
+            test_flags |= SCRIPT_VERIFY_P2SH;
+        }
+        bool ret = CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, nullptr);
+        // CheckInputs should succeed iff test_flags doesn't intersect with
+        // failing_flags
+        bool expected_return_value = !(test_flags & failing_flags);
+        if (expected_return_value && upgraded_nop) {
+            // If the script flag being tested corresponds to an upgraded NOP,
+            // then script execution should fail if DISCOURAGE_UPGRADABLE_NOPS
+            // is set.
+            expected_return_value = !(test_flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS);
+        }
+        BOOST_CHECK_EQUAL(ret, expected_return_value);
+
+        // Test the caching
+        if (ret && add_to_cache) {
+            // Check that we get a cache hit if the tx was valid
+            std::vector<CScriptCheck> scriptchecks;
+            BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, &scriptchecks));
+            BOOST_CHECK(scriptchecks.empty());
+        } else {
+            // Check that we get script executions to check, if the transaction
+            // was invalid, or we didn't add to cache.
+            std::vector<CScriptCheck> scriptchecks;
+            BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, test_flags, true, add_to_cache, txdata, &scriptchecks));
+            BOOST_CHECK_EQUAL(scriptchecks.size(), tx.vin.size());
+        }
+    }
+}
+
+BOOST_FIXTURE_TEST_CASE(checkinputs_test, TestChain100Setup)
+{
+    // Test that passing CheckInputs with one set of script flags doesn't imply
+    // that we would pass again with a different set of flags.
+    InitScriptExecutionCache();
+
+    CScript p2pk_scriptPubKey = CScript() << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+    CScript p2sh_scriptPubKey = GetScriptForDestination(CScriptID(p2pk_scriptPubKey));
+    CScript p2pkh_scriptPubKey = GetScriptForDestination(coinbaseKey.GetPubKey().GetID());
+    CScript p2wpkh_scriptPubKey = GetScriptForWitness(p2pkh_scriptPubKey);
+
+    CBasicKeyStore keystore;
+    keystore.AddKey(coinbaseKey);
+    keystore.AddCScript(p2pk_scriptPubKey);
+
+    // flags to test: SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, SCRIPT_VERIFY_CHECKSEQUENCE_VERIFY, SCRIPT_VERIFY_NULLDUMMY, uncompressed pubkey thing
+
+    // Create 2 outputs that match the three scripts above, spending the first
+    // coinbase tx.
+    CMutableTransaction spend_tx;
+
+    spend_tx.nVersion = 1;
+    spend_tx.vin.resize(1);
+    spend_tx.vin[0].prevout.hash = coinbaseTxns[0].GetHash();
+    spend_tx.vin[0].prevout.n = 0;
+    spend_tx.vout.resize(4);
+    spend_tx.vout[0].nValue = 11*CENT;
+    spend_tx.vout[0].scriptPubKey = p2sh_scriptPubKey;
+    spend_tx.vout[1].nValue = 11*CENT;
+    spend_tx.vout[1].scriptPubKey = p2wpkh_scriptPubKey;
+    spend_tx.vout[2].nValue = 11*CENT;
+    spend_tx.vout[2].scriptPubKey = CScript() << OP_CHECKLOCKTIMEVERIFY << OP_DROP << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+    spend_tx.vout[3].nValue = 11*CENT;
+    spend_tx.vout[3].scriptPubKey = CScript() << OP_CHECKSEQUENCEVERIFY << OP_DROP << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
+
+    // Sign, with a non-DER signature
+    {
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(p2pk_scriptPubKey, spend_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char) 0); // padding byte makes this non-DER
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        spend_tx.vin[0].scriptSig << vchSig;
+    }
+
+    LOCK(cs_main);
+
+    // Test that invalidity under a set of flags doesn't preclude validity
+    // under other (eg consensus) flags.
+    // spend_tx is invalid according to DERSIG
+    CValidationState state;
+    {
+        PrecomputedTransactionData ptd_spend_tx(spend_tx);
+
+        BOOST_CHECK(!CheckInputs(spend_tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, nullptr));
+
+        // If we call again asking for scriptchecks (as happens in
+        // ConnectBlock), we should add a script check object for this -- we're
+        // not caching invalidity (if that changes, delete this test case).
+        std::vector<CScriptCheck> scriptchecks;
+        BOOST_CHECK(CheckInputs(spend_tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_DERSIG, true, true, ptd_spend_tx, &scriptchecks));
+        BOOST_CHECK_EQUAL(scriptchecks.size(), 1);
+
+        // Test that CheckInputs returns true iff DERSIG-enforcing flags are
+        // not present.  Don't add these checks to the cache, so that we can
+        // test later that block validation works fine in the absence of cached
+        // successes.
+        ValidateCheckInputsForAllFlags(spend_tx, SCRIPT_VERIFY_DERSIG | SCRIPT_VERIFY_LOW_S | SCRIPT_VERIFY_STRICTENC, false, false);
+
+        // And if we produce a block with this tx, it should be valid (DERSIG not
+        // enabled yet), even though there's no cache entry.
+        CBlock block;
+
+        block = CreateAndProcessBlock({spend_tx}, p2pk_scriptPubKey);
+        BOOST_CHECK(chainActive.Tip()->GetBlockHash() == block.GetHash());
+        BOOST_CHECK(pcoinsTip->GetBestBlock() == block.GetHash());
+    }
+
+    // Test P2SH: construct a transaction that is valid without P2SH, and
+    // then test validity with P2SH.
+    {
+        CMutableTransaction invalid_under_p2sh_tx;
+        invalid_under_p2sh_tx.nVersion = 1;
+        invalid_under_p2sh_tx.vin.resize(1);
+        invalid_under_p2sh_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_under_p2sh_tx.vin[0].prevout.n = 0;
+        invalid_under_p2sh_tx.vout.resize(1);
+        invalid_under_p2sh_tx.vout[0].nValue = 11*CENT;
+        invalid_under_p2sh_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+        std::vector<unsigned char> vchSig2(p2pk_scriptPubKey.begin(), p2pk_scriptPubKey.end());
+        invalid_under_p2sh_tx.vin[0].scriptSig << vchSig2;
+
+        ValidateCheckInputsForAllFlags(invalid_under_p2sh_tx, SCRIPT_VERIFY_P2SH, true, false);
+    }
+
+    // Test CHECKLOCKTIMEVERIFY
+    {
+        CMutableTransaction invalid_with_cltv_tx;
+        invalid_with_cltv_tx.nVersion = 1;
+        invalid_with_cltv_tx.nLockTime = 100;
+        invalid_with_cltv_tx.vin.resize(1);
+        invalid_with_cltv_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_with_cltv_tx.vin[0].prevout.n = 2;
+        invalid_with_cltv_tx.vin[0].nSequence = 0;
+        invalid_with_cltv_tx.vout.resize(1);
+        invalid_with_cltv_tx.vout[0].nValue = 11*CENT;
+        invalid_with_cltv_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(spend_tx.vout[2].scriptPubKey, invalid_with_cltv_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 101;
+
+        ValidateCheckInputsForAllFlags(invalid_with_cltv_tx, SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true);
+
+        // Make it valid, and check again
+        invalid_with_cltv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
+        CValidationState state;
+        PrecomputedTransactionData txdata(invalid_with_cltv_tx);
+        BOOST_CHECK(CheckInputs(invalid_with_cltv_tx, state, pcoinsTip, true, SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY, true, true, txdata, nullptr));
+    }
+
+    // TEST CHECKSEQUENCEVERIFY
+    {
+        CMutableTransaction invalid_with_csv_tx;
+        invalid_with_csv_tx.nVersion = 2;
+        invalid_with_csv_tx.vin.resize(1);
+        invalid_with_csv_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        invalid_with_csv_tx.vin[0].prevout.n = 3;
+        invalid_with_csv_tx.vin[0].nSequence = 100;
+        invalid_with_csv_tx.vout.resize(1);
+        invalid_with_csv_tx.vout[0].nValue = 11*CENT;
+        invalid_with_csv_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        std::vector<unsigned char> vchSig;
+        uint256 hash = SignatureHash(spend_tx.vout[3].scriptPubKey, invalid_with_csv_tx, 0, SIGHASH_ALL, 0, SIGVERSION_BASE);
+        BOOST_CHECK(coinbaseKey.Sign(hash, vchSig));
+        vchSig.push_back((unsigned char)SIGHASH_ALL);
+        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 101;
+
+        ValidateCheckInputsForAllFlags(invalid_with_csv_tx, SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true);
+
+        // Make it valid, and check again
+        invalid_with_csv_tx.vin[0].scriptSig = CScript() << vchSig << 100;
+        CValidationState state;
+        PrecomputedTransactionData txdata(invalid_with_csv_tx);
+        BOOST_CHECK(CheckInputs(invalid_with_csv_tx, state, pcoinsTip, true, SCRIPT_VERIFY_CHECKSEQUENCEVERIFY, true, true, txdata, nullptr));
+    }
+
+    // TODO: add tests for remaining script flags
+
+    // Test that passing CheckInputs with a valid witness doesn't imply success
+    // for the same tx with a different witness.
+    {
+        CMutableTransaction valid_with_witness_tx;
+        valid_with_witness_tx.nVersion = 1;
+        valid_with_witness_tx.vin.resize(1);
+        valid_with_witness_tx.vin[0].prevout.hash = spend_tx.GetHash();
+        valid_with_witness_tx.vin[0].prevout.n = 1;
+        valid_with_witness_tx.vout.resize(1);
+        valid_with_witness_tx.vout[0].nValue = 11*CENT;
+        valid_with_witness_tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        SignatureData sigdata;
+        ProduceSignature(MutableTransactionSignatureCreator(&keystore, &valid_with_witness_tx, 0, 11*CENT, SIGHASH_ALL), spend_tx.vout[1].scriptPubKey, sigdata);
+        UpdateTransaction(valid_with_witness_tx, 0, sigdata);
+
+        // This should be valid under all script flags.
+        ValidateCheckInputsForAllFlags(valid_with_witness_tx, 0, true, false);
+
+        // Remove the witness, and check that it is now invalid.
+        valid_with_witness_tx.vin[0].scriptWitness.SetNull();
+        ValidateCheckInputsForAllFlags(valid_with_witness_tx, SCRIPT_VERIFY_WITNESS, true, false);
+    }
+
+    {
+        // Test a transaction with multiple inputs.
+        CMutableTransaction tx;
+
+        tx.nVersion = 1;
+        tx.vin.resize(2);
+        tx.vin[0].prevout.hash = spend_tx.GetHash();
+        tx.vin[0].prevout.n = 0;
+        tx.vin[1].prevout.hash = spend_tx.GetHash();
+        tx.vin[1].prevout.n = 1;
+        tx.vout.resize(1);
+        tx.vout[0].nValue = 22*CENT;
+        tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
+
+        // Sign
+        for (int i=0; i<2; ++i) {
+            SignatureData sigdata;
+            ProduceSignature(MutableTransactionSignatureCreator(&keystore, &tx, i, 11*CENT, SIGHASH_ALL), spend_tx.vout[i].scriptPubKey, sigdata);
+            UpdateTransaction(tx, i, sigdata);
+        }
+
+        // This should be valid under all script flags
+        ValidateCheckInputsForAllFlags(tx, 0, true, false);
+
+        // Check that if the second input is invalid, but the first input is
+        // valid, the transaction is not cached.
+        // Invalidate vin[1]
+        tx.vin[1].scriptWitness.SetNull();
+
+        CValidationState state;
+        PrecomputedTransactionData txdata(tx);
+        // This transaction is now invalid under segwit, because of the second input.
+        BOOST_CHECK(!CheckInputs(tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, nullptr));
+
+        std::vector<CScriptCheck> scriptchecks;
+        // Make sure this transaction was not cached (ie because the first
+        // input was valid)
+        BOOST_CHECK(CheckInputs(tx, state, pcoinsTip, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS, true, true, txdata, &scriptchecks));
+        // Should get 2 script checks back -- caching is on a whole-transaction basis.
+        BOOST_CHECK_EQUAL(scriptchecks.size(), 2);
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/validation.cpp b/src/validation.cpp
diff --git a/src/validation.h b/src/validation.h

Original file line number	Diff line number	Diff line change
`@@ -447,7 +447,7 @@ std::string HelpMessage(HelpMessageMode mode)`
`447`	`447`	`{`
`448`	`448`	`strUsage += HelpMessageOpt("-logtimemicros", strprintf("Add microsecond precision to debug timestamps (default: %u)", DEFAULT_LOGTIMEMICROS));`
`449`	`449`	`strUsage += HelpMessageOpt("-mocktime=<n>", "Replace actual time with <n> seconds since epoch (default: 0)");`
`450`		`- strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit size of signature cache to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));`
	`450`	`+ strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit sum of signature cache and script execution cache sizes to <n> MiB (default: %u)", DEFAULT_MAX_SIG_CACHE_SIZE));`
`451`	`451`	`strUsage += HelpMessageOpt("-maxtipage=<n>", strprintf("Maximum tip age in seconds to consider node in initial block download (default: %u)", DEFAULT_MAX_TIP_AGE));`
`452`	`452`	`}`
`453`	`453`	`strUsage += HelpMessageOpt("-maxtxfee=<amt>", strprintf(_("Maximum total fees (in %s) to use in a single wallet transaction or raw transaction; setting this too low may abort large transactions (default: %s)"),`
`@@ -1191,6 +1191,7 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)`
`1191`	`1191`	`LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);`
`1192`	`1192`
`1193`	`1193`	`InitSignatureCache();`
	`1194`	`+ InitScriptExecutionCache();`
`1194`	`1195`
`1195`	`1196`	`LogPrintf("Using %u threads for script verification\n", nScriptCheckThreads);`
`1196`	`1197`	`if (nScriptCheckThreads) {`
Original file line number	Diff line number	Diff line change
`@@ -74,10 +74,10 @@ void InitSignatureCache()`
`74`	`74`	`{`
`75`	`75`	`// nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,`
`76`	`76`	`// setup_bytes creates the minimum possible cache (2 elements).`
`77`		`- size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE)), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);`
	`77`	`+ size_t nMaxCacheSize = std::min(std::max((int64_t)0, GetArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);`
`78`	`78`	`size_t nElems = signatureCache.setup_bytes(nMaxCacheSize);`
`79`		`- LogPrintf("Using %zu MiB out of %zu requested for signature cache, able to store %zu elements\n",`
`80`		`- (nElems*sizeof(uint256)) >>20, nMaxCacheSize>>20, nElems);`
	`79`	`+ LogPrintf("Using %zu MiB out of %zu/2 requested for signature cache, able to store %zu elements\n",`
	`80`	`+ (nElemssizeof(uint256)) >>20, (nMaxCacheSize2)>>20, nElems);`
`81`	`81`	`}`
`82`	`82`
`83`	`83`	`bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const`