Add header::difficulty().

Author: evoskuil

include/bitcoin/system/chain/header.hpp

@@ -81,7 +81,6 @@ class BC_API header
     void to_data(std::ostream& stream) const NOEXCEPT;
     void to_data(writer& sink) const NOEXCEPT;
 
-
     /// Properties.
     /// -----------------------------------------------------------------------
     /// Native properties.
@@ -96,6 +95,7 @@ class BC_API header
     /// Computed properties.
     uint256_t proof() const NOEXCEPT;
     hash_digest hash() const NOEXCEPT;
+    double difficulty() const NOEXCEPT;
 
     /// Cache and metadata.
     /// -----------------------------------------------------------------------

src/chain/header.cpp

@@ -268,6 +268,29 @@ hash_digest header::hash() const NOEXCEPT
     return digest;
 }
 
+// computed, not used in consensus.
+double header::difficulty() const NOEXCEPT
+{
+    auto shift = bit_and(shift_right(bits_, 24), 0xff_u32);
+    auto difference =
+        static_cast<double>(0x0000ffff_u32) /
+        static_cast<double>(bit_and(bits_, 0x00ffffff_u32));
+
+    while (shift < 29u)
+    {
+        difference *= 256.0;
+        ++shift;
+    }
+
+    while (shift > 29u)
+    {
+        difference /= 256.0;
+        --shift;
+    }
+
+    return difference;
+}
+
 // Cache and metadata.
 // ----------------------------------------------------------------------------
 

test/chain/header.cpp

@@ -240,14 +240,20 @@ BOOST_AUTO_TEST_CASE(header__to_data__writer__expected)
 // properties
 // ----------------------------------------------------------------------------
 
-// hash
-
 BOOST_AUTO_TEST_CASE(header__proof__genesis_block__expected)
 {
     const chain::block block{ settings(selection::mainnet).genesis_block };
     BOOST_REQUIRE_EQUAL(block.header().proof(), 0x0000000100010001);
 }
 
+// hash
+
+BOOST_AUTO_TEST_CASE(header__difficulty__genesis_block__expected)
+{
+    const chain::block block{ settings(selection::mainnet).genesis_block };
+    BOOST_REQUIRE_EQUAL(block.header().difficulty(), 1.0);
+}
+
 // validation (public)
 // ----------------------------------------------------------------------------