Merge pull request libbitcoin#1581 from evoskuil/master

Add block.spends computed count of non-null inputs.

Author: evoskuil

include/bitcoin/system/chain/block.hpp

@@ -90,6 +90,7 @@ class BC_API block
     hashes transaction_hashes(bool witness) const NOEXCEPT;
 
     /// Computed properties.
+    size_t spends() const NOEXCEPT;
     size_t weight() const NOEXCEPT;
     uint64_t fees() const NOEXCEPT;
     uint64_t claim() const NOEXCEPT;

include/bitcoin/system/chain/prevout.hpp

@@ -40,7 +40,7 @@ class BC_API prevout final
         size_t height;
 
         /// database: populated with a database identifier for the parent tx.
-        uint64_t parent{ zero };
+        uint32_t parent{ zero };
     };
 
     ///************************************************************************

src/chain/block.cpp

@@ -251,6 +251,21 @@ hashes block::transaction_hashes(bool witness) const NOEXCEPT
     return out;
 }
 
+// computed
+size_t block::spends() const NOEXCEPT
+{
+    if (txs_->empty())
+        return zero;
+
+    // Overflow returns max_size_t.
+    const auto ins = [](size_t total, const auto& tx) NOEXCEPT
+    {
+         return ceilinged_add(total, tx->inputs());
+    };
+
+    return std::accumulate(std::next(txs_->begin()), txs_->end(), zero, ins);
+}
+
 // computed
 hash_digest block::hash() const NOEXCEPT
 {

test/chain/block.cpp

@@ -440,6 +440,17 @@ BOOST_AUTO_TEST_CASE(block__to_data__writer__expected)
 // fees
 // claim
 
+BOOST_AUTO_TEST_CASE(block__spends__genesis__zero)
+{
+    const auto genesis = settings(selection::mainnet).genesis_block;
+    BOOST_REQUIRE(is_zero(genesis.spends()));
+}
+
+BOOST_AUTO_TEST_CASE(block__spends__coinbase_only__zero)
+{
+    BOOST_REQUIRE(is_zero(get_block().spends()));
+}
+
 BOOST_AUTO_TEST_CASE(block__hash__default__matches_header_hash)
 {
     const block instance;