Merge pull request #1571 from evoskuil/master

Add math left_zeros, right_zeros, left_ones, right_ones.

Author: evoskuil

include/bitcoin/system/chain/block.hpp

@@ -137,7 +137,7 @@ class BC_API block
     code confirm(const context& ctx) const NOEXCEPT;
 
     /// Populate previous outputs (only, no metadata) internal to the block.
-    void populate() const NOEXCEPT;
+    size_t populate() const NOEXCEPT;
 
 protected:
     block(const chain::header::cptr& header,

include/bitcoin/system/impl/math/bits.ipp

@@ -49,6 +49,30 @@ constexpr size_t bit_width(Value value) NOEXCEPT
     return is_negative(value) ? bits<Value> : bit_width(to_unsigned(value));
 }
 
+template <typename Value, if_unsigned_integer<Value>>
+constexpr size_t left_zeros(Value value) NOEXCEPT
+{
+    return to_unsigned(std::countl_zero<Value>(value));
+}
+
+template <typename Value, if_unsigned_integer<Value>>
+constexpr size_t right_zeros(Value value) NOEXCEPT
+{
+    return to_unsigned(std::countr_zero<Value>(value));
+}
+
+template <typename Value, if_unsigned_integer<Value>>
+constexpr size_t left_ones(Value value) NOEXCEPT
+{
+    return to_unsigned(std::countl_one<Value>(value));
+}
+
+template <typename Value, if_unsigned_integer<Value>>
+constexpr size_t right_ones(Value value) NOEXCEPT
+{
+    return to_unsigned(std::countr_one<Value>(value));
+}
+
 // Bitwise logical operations.
 // ----------------------------------------------------------------------------
 

include/bitcoin/system/math/bits.hpp

@@ -39,6 +39,18 @@ constexpr size_t bit_width(Value value) NOEXCEPT;
 template <typename Value, if_signed_integer<Value> = true>
 constexpr size_t bit_width(Value value) NOEXCEPT;
 
+// Because std::countl_* (C++20) functions return int.
+template <typename Value, if_unsigned_integer<Value> = true>
+constexpr size_t left_zeros(Value value) NOEXCEPT;
+template <typename Value, if_unsigned_integer<Value> = true>
+constexpr size_t right_zeros(Value value) NOEXCEPT;
+
+// Because std::countr_* (C++20) functions return int.
+template <typename Value, if_unsigned_integer<Value> = true>
+constexpr size_t left_ones(Value value) NOEXCEPT;
+template <typename Value, if_unsigned_integer<Value> = true>
+constexpr size_t right_ones(Value value) NOEXCEPT;
+
 /// Bitwise logical operations.
 /// ---------------------------------------------------------------------------
 

src/chain/block.cpp

@@ -688,7 +688,7 @@ bool block::is_unspent_coinbase_collision() const NOEXCEPT
 }
 
 // Search is not ordered, forward references are caught by block.check.
-void block::populate() const NOEXCEPT
+size_t block::populate() const NOEXCEPT
 {
     std::unordered_map<point, output::cptr> points{};
     uint32_t index{};
@@ -699,16 +699,22 @@ void block::populate() const NOEXCEPT
             points.emplace(std::pair{ point{ (*tx)->hash(false), index++ },
                 out });
 
-    // Populate input prevouts from hash table.
+    // Populate input prevouts from hash table and obtain count.
+    size_t count{};
     for (auto tx = txs_->begin(); tx != txs_->end(); ++tx)
     {
         for (const auto& in: *(*tx)->inputs_ptr())
         {
             const auto point = points.find(in->point());
             if (point != points.end())
+            {
+                ++count;
                 in->prevout = point->second;
+            }
         }
     }
+
+    return count;
 }
 
 // Delegated.

test/math/bits.cpp

@@ -111,6 +111,30 @@ static_assert(bit_width<int64_t>(0x800000000000_ni64) == 64u);
 static_assert(bit_width<int64_t>(0x80010000000000_ni64) == 64u);
 static_assert(bit_width<int64_t>(0x8000000000000000_ni64) == 64u);
 
+// zeroes
+
+static_assert(left_zeros(uint8_t{ 0b00000000 }) == 8);
+static_assert(left_zeros(uint8_t{ 0b11111111 }) == 0);
+static_assert(left_zeros(uint8_t{ 0b11110000 }) == 0);
+static_assert(left_zeros(uint8_t{ 0b00011110 }) == 3);
+
+static_assert(right_zeros(uint8_t{ 0b00000000 }) == 8);
+static_assert(right_zeros(uint8_t{ 0b11111111 }) == 0);
+static_assert(right_zeros(uint8_t{ 0b00011100 }) == 2);
+static_assert(right_zeros(uint8_t{ 0b00011101 }) == 0);
+
+// ones
+
+static_assert(left_ones(uint8_t{ 0b00000000 }) == 0);
+static_assert(left_ones(uint8_t{ 0b11111111 }) == 8);
+static_assert(left_ones(uint8_t{ 0b01111111 }) == 0);
+static_assert(left_ones(uint8_t{ 0b11100011 }) == 3);
+
+static_assert(right_ones(uint8_t{ 0b00000000 }) == 0);
+static_assert(right_ones(uint8_t{ 0b11111111 }) == 8);
+static_assert(right_ones(uint8_t{ 0b11111110 }) == 0);
+static_assert(right_ones(uint8_t{ 0b11100011 }) == 2);
+
 // ones_complement (NOT)
 // inverts all bits (~n, !bool)
 static_assert(bit_not(-4) == 3);