Improve STVector256 deserialization

src/ripple/basics/Slice.h

@@ -48,7 +48,8 @@ private:
     std::size_t size_ = 0;
 
 public:
-    using const_iterator = std::uint8_t const*;
+    using value_type = std::uint8_t;
+    using const_iterator = value_type const*;
 
     /** Default constructed Slice has length 0. */
     Slice() noexcept = default;
@@ -75,13 +76,13 @@ public:
         This may be zero for an empty range.
     */
     /** @{ */
-    std::size_t
+    [[nodiscard]] std::size_t
     size() const noexcept
     {
         return size_;
     }
 
-    std::size_t
+    [[nodiscard]] std::size_t
     length() const noexcept
     {
         return size_;

src/ripple/basics/base_uint.h

@@ -26,6 +26,7 @@
 #define RIPPLE_BASICS_BASE_UINT_H_INCLUDED
 
 #include <ripple/basics/Expected.h>
+#include <ripple/basics/Slice.h>
 #include <ripple/basics/contract.h>
 #include <ripple/basics/hardened_hash.h>
 #include <ripple/basics/strHex.h>
@@ -56,6 +57,11 @@ struct is_contiguous_container<
 {
 };
 
+template <>
+struct is_contiguous_container<Slice> : std::true_type
+{
+};
+
 }  // namespace detail
 
 /** Integers of any length that is a multiple of 32-bits

src/ripple/protocol/impl/STVector256.cpp

@@ -26,19 +26,19 @@ namespace ripple {
 
 STVector256::STVector256(SerialIter& sit, SField const& name) : STBase(name)
 {
-    Blob data = sit.getVL();
-    auto const count = data.size() / (256 / 8);
-    mValue.reserve(count);
-    Blob::iterator begin = data.begin();
-    unsigned int uStart = 0;
-    for (unsigned int i = 0; i != count; i++)
-    {
-        unsigned int uEnd = uStart + (256 / 8);
-        // This next line could be optimized to construct a default
-        // uint256 in the vector and then copy into it
-        mValue.push_back(uint256(Blob(begin + uStart, begin + uEnd)));
-        uStart = uEnd;
-    }
+    auto const slice = sit.getSlice(sit.getVLDataLength());
+
+    if (slice.size() % uint256::size() != 0)
+        Throw<std::runtime_error>(
+            "Bad serialization for STVector256: " +
+            std::to_string(slice.size()));
+
+    auto const cnt = slice.size() / uint256::size();
+
+    mValue.reserve(cnt);
+
+    for (std::size_t i = 0; i != cnt; ++i)
+        mValue.emplace_back(slice.substr(i * uint256::size(), uint256::size()));
 }
 
 STBase*