rct: add a zeroCommit cache for common pre-rct case

This is called for every pre-rct output at blockchain sync time,
and a lot of them wil hit the cache, saving a scalarmult each.

3 files changed, 25 insertions, 0 deletions

diff --git a/tests/performance_tests/crypto_ops.h b/tests/performance_tests/crypto_ops.h
index 3c68583c5..25ab008db 100644
--- a/tests/performance_tests/crypto_ops.h
+++ b/tests/performance_tests/crypto_ops.h
@@ -40,6 +40,7 @@ enum test_op
   op_sc_mul,
   op_ge_add_raw,
   op_ge_add_p3_p3,
+  op_zeroCommitCached,
   ops_fast,
 
   op_addKeys,
@@ -54,6 +55,7 @@ enum test_op
   op_addKeys3,
   op_addKeys3_2,
   op_isInMainSubgroup,
+  op_zeroCommitUncached,
 };
 
 template<test_op op>
@@ -108,6 +110,8 @@ public:
       case op_addKeys3: rct::addKeys3(key, scalar0, point0, scalar1, precomp1); break;
       case op_addKeys3_2: rct::addKeys3(key, scalar0, precomp0, scalar1, precomp1); break;
       case op_isInMainSubgroup: rct::isInMainSubgroup(point0); break;
+      case op_zeroCommitUncached: rct::zeroCommit(9001); break;
+      case op_zeroCommitCached: rct::zeroCommit(9000); break;
       default: return false;
     }
     return true;
diff --git a/tests/performance_tests/main.cpp b/tests/performance_tests/main.cpp
index 87a1573c2..3c71cb99f 100644
--- a/tests/performance_tests/main.cpp
+++ b/tests/performance_tests/main.cpp
@@ -256,6 +256,8 @@ int main(int argc, char** argv)
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_addKeys3);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_addKeys3_2);
   TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_isInMainSubgroup);
+  TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_zeroCommitUncached);
+  TEST_PERFORMANCE1(filter, p, test_crypto_ops, op_zeroCommitCached);
 
   TEST_PERFORMANCE2(filter, p, test_multiexp, multiexp_bos_coster, 2);
   TEST_PERFORMANCE2(filter, p, test_multiexp, multiexp_bos_coster, 4);
diff --git a/tests/unit_tests/ringct.cpp b/tests/unit_tests/ringct.cpp
index 3877ef785..52bdb00cf 100644
--- a/tests/unit_tests/ringct.cpp
+++ b/tests/unit_tests/ringct.cpp
@@ -1086,6 +1086,25 @@ TEST(ringct, zeroCommmit)
   ASSERT_EQ(z, manual);
 }
 
+static rct::key uncachedZeroCommit(uint64_t amount)
+{
+  const rct::key am = rct::d2h(amount);
+  const rct::key bH = rct::scalarmultH(am);
+  return rct::addKeys(rct::G, bH);
+}
+
+TEST(ringct, zeroCommitCache)
+{
+  ASSERT_EQ(rct::zeroCommit(0), uncachedZeroCommit(0));
+  ASSERT_EQ(rct::zeroCommit(1), uncachedZeroCommit(1));
+  ASSERT_EQ(rct::zeroCommit(2), uncachedZeroCommit(2));
+  ASSERT_EQ(rct::zeroCommit(10), uncachedZeroCommit(10));
+  ASSERT_EQ(rct::zeroCommit(200), uncachedZeroCommit(200));
+  ASSERT_EQ(rct::zeroCommit(1000000000), uncachedZeroCommit(1000000000));
+  ASSERT_EQ(rct::zeroCommit(3000000000000), uncachedZeroCommit(3000000000000));
+  ASSERT_EQ(rct::zeroCommit(900000000000000), uncachedZeroCommit(900000000000000));
+}
+
 TEST(ringct, H)
 {
   ge_p3 p3;