refactor: Change base_blob::SetHex() to take std::string_view

Clarify that hex strings are parsed as little-endian.

Author: hodlinator

src/test/uint256_tests.cpp

@@ -58,13 +58,8 @@ static std::string ArrayToString(const unsigned char A[], unsigned int width)
     return Stream.str();
 }
 
-inline uint160 uint160S(const char *str)
-{
-    uint160 rv;
-    rv.SetHex(str);
-    return rv;
-}
-inline uint160 uint160S(const std::string& str)
+// Input is treated as little-endian.
+inline uint160 uint160S(std::string_view str)
 {
     uint160 rv;
     rv.SetHex(str);
@@ -156,6 +151,10 @@ BOOST_AUTO_TEST_CASE( comparison ) // <= >= < >
     BOOST_CHECK_LT(OneS, MaxS);
     BOOST_CHECK_LT(R1S, MaxS);
     BOOST_CHECK_LT(R2S, MaxS);
+
+    // Verify hex strings are little-endian
+    BOOST_CHECK_LT(uint256S("2000000000000000000000000000000000000000000000000000000000000001"),
+                   uint256S("1000000000000000000000000000000000000000000000000000000000000002"));
 }
 
 BOOST_AUTO_TEST_CASE( methods ) // GetHex SetHex begin() end() size() GetLow64 GetSerializeSize, Serialize, Unserialize

src/uint256.cpp

@@ -18,39 +18,31 @@ std::string base_blob<BITS>::GetHex() const
 }
 
 template <unsigned int BITS>
-void base_blob<BITS>::SetHex(const char* psz)
+void base_blob<BITS>::SetHex(const std::string_view str)
 {
     std::fill(m_data.begin(), m_data.end(), 0);
 
-    // skip leading spaces
-    while (IsSpace(*psz))
-        psz++;
+    const auto trimmed = util::RemovePrefixView(util::TrimStringView(str), "0x");
 
-    // skip 0x
-    if (psz[0] == '0' && ToLower(psz[1]) == 'x')
-        psz += 2;
-
-    // hex string to uint
+    // Note: if we are passed a greater number of digits than would fit as bytes
+    // in m_data, we will be discarding the leftmost ones.
+    // str="12bc" in a WIDTH=1 m_data => m_data[] == "\0xbc", not "0x12".
     size_t digits = 0;
-    while (::HexDigit(psz[digits]) != -1)
-        digits++;
+    for (const char c : trimmed) {
+        if (::HexDigit(c) == -1) break;
+        ++digits;
+    }
     unsigned char* p1 = m_data.data();
     unsigned char* pend = p1 + WIDTH;
     while (digits > 0 && p1 < pend) {
-        *p1 = ::HexDigit(psz[--digits]);
+        *p1 = ::HexDigit(trimmed[--digits]);
         if (digits > 0) {
-            *p1 |= ((unsigned char)::HexDigit(psz[--digits]) << 4);
+            *p1 |= ((unsigned char)::HexDigit(trimmed[--digits]) << 4);
             p1++;
         }
     }
 }
 
-template <unsigned int BITS>
-void base_blob<BITS>::SetHex(const std::string& str)
-{
-    SetHex(str.c_str());
-}
-
 template <unsigned int BITS>
 std::string base_blob<BITS>::ToString() const
 {
@@ -60,14 +52,12 @@ std::string base_blob<BITS>::ToString() const
 // Explicit instantiations for base_blob<160>
 template std::string base_blob<160>::GetHex() const;
 template std::string base_blob<160>::ToString() const;
-template void base_blob<160>::SetHex(const char*);
-template void base_blob<160>::SetHex(const std::string&);
+template void base_blob<160>::SetHex(std::string_view);
 
 // Explicit instantiations for base_blob<256>
 template std::string base_blob<256>::GetHex() const;
 template std::string base_blob<256>::ToString() const;
-template void base_blob<256>::SetHex(const char*);
-template void base_blob<256>::SetHex(const std::string&);
+template void base_blob<256>::SetHex(std::string_view);
 
 const uint256 uint256::ZERO(0);
 const uint256 uint256::ONE(1);

src/uint256.h

@@ -57,9 +57,9 @@ class base_blob
     friend constexpr bool operator!=(const base_blob& a, const base_blob& b) { return a.Compare(b) != 0; }
     friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }
 
+    // Hex string representations are little-endian.
     std::string GetHex() const;
-    void SetHex(const char* psz);
-    void SetHex(const std::string& str);
+    void SetHex(std::string_view str);
     std::string ToString() const;
 
     constexpr const unsigned char* data() const { return m_data.data(); }
@@ -112,21 +112,11 @@ class uint256 : public base_blob<256> {
     static const uint256 ONE;
 };
 
-/* uint256 from const char *.
- * This is a separate function because the constructor uint256(const char*) can result
- * in dangerously catching uint256(0).
+/* uint256 from std::string_view, treated as little-endian.
+ * This is not a uint256 constructor because of historical fears of uint256(0)
+ * resolving to a NULL string and crashing.
  */
-inline uint256 uint256S(const char *str)
-{
-    uint256 rv;
-    rv.SetHex(str);
-    return rv;
-}
-/* uint256 from std::string.
- * This is a separate function because the constructor uint256(const std::string &str) can result
- * in dangerously catching uint256(0) via std::string(const char*).
- */
-inline uint256 uint256S(const std::string& str)
+inline uint256 uint256S(std::string_view str)
 {
     uint256 rv;
     rv.SetHex(str);