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;

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
 {