From ee3abdbe6f116bf8072fb8ba5218d278c8449da8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Bylica?= <chfast@gmail.com>
Date: Thu, 12 May 2022 22:54:08 +0200
Subject: [PATCH] C++: Rework hex literals parsing

---
 include/evmc/evmc.hpp | 69 +++++++++++--------------------------------
 include/evmc/hex.hpp  |  8 ++---
 2 files changed, 22 insertions(+), 55 deletions(-)

diff --git a/include/evmc/evmc.hpp b/include/evmc/evmc.hpp
index 57f0faa9d..7afffacd4 100644
--- a/include/evmc/evmc.hpp
+++ b/include/evmc/evmc.hpp
@@ -5,6 +5,7 @@
 
 #include <evmc/evmc.h>
 #include <evmc/helpers.h>
+#include <evmc/hex.hpp>
 
 #include <functional>
 #include <initializer_list>
@@ -280,71 +281,37 @@ inline constexpr bytes32::operator bool() const noexcept
 
 namespace literals
 {
-namespace internal
-{
-constexpr int from_hex(char c) noexcept
-{
-    return (c >= 'a' && c <= 'f') ? c - ('a' - 10) :
-           (c >= 'A' && c <= 'F') ? c - ('A' - 10) :
-                                    c - '0';
-}
-
-constexpr uint8_t byte(const char* s, size_t i) noexcept
-{
-    return static_cast<uint8_t>((from_hex(s[2 * i]) << 4) | from_hex(s[2 * i + 1]));
-}
+/// Breaks compilation and reports error string in constexpr context.
+inline void error([[maybe_unused]] const char* message) noexcept {}
 
+/// Converts a raw literal into value of type T.
 template <typename T>
-T from_hex(const char*) noexcept;
-
-template <>
-constexpr bytes32 from_hex<bytes32>(const char* s) noexcept
-{
-    return {
-        {{byte(s, 0),  byte(s, 1),  byte(s, 2),  byte(s, 3),  byte(s, 4),  byte(s, 5),  byte(s, 6),
-          byte(s, 7),  byte(s, 8),  byte(s, 9),  byte(s, 10), byte(s, 11), byte(s, 12), byte(s, 13),
-          byte(s, 14), byte(s, 15), byte(s, 16), byte(s, 17), byte(s, 18), byte(s, 19), byte(s, 20),
-          byte(s, 21), byte(s, 22), byte(s, 23), byte(s, 24), byte(s, 25), byte(s, 26), byte(s, 27),
-          byte(s, 28), byte(s, 29), byte(s, 30), byte(s, 31)}}};
-}
-
-template <>
-constexpr address from_hex<address>(const char* s) noexcept
+constexpr T to(std::string_view s) noexcept
 {
-    return {
-        {{byte(s, 0),  byte(s, 1),  byte(s, 2),  byte(s, 3),  byte(s, 4),  byte(s, 5),  byte(s, 6),
-          byte(s, 7),  byte(s, 8),  byte(s, 9),  byte(s, 10), byte(s, 11), byte(s, 12), byte(s, 13),
-          byte(s, 14), byte(s, 15), byte(s, 16), byte(s, 17), byte(s, 18), byte(s, 19)}}};
-}
+    if (s == "0")
+        return T{};
 
-template <typename T, char... c>
-constexpr T from_literal() noexcept
-{
-    constexpr auto size = sizeof...(c);
-    constexpr char literal[] = {c...};
-    constexpr bool is_simple_zero = size == 1 && literal[0] == '0';
+    if (s[0] != '0' || s[1] != 'x')
+        error("literal must be in hexadecimal notation");
 
-    static_assert(is_simple_zero || (literal[0] == '0' && literal[1] == 'x'),
-                  "literal must be in hexadecimal notation");
-    static_assert(is_simple_zero || size == 2 * sizeof(T) + 2,
-                  "literal must match the result type size");
+    if (s.length() != 2 * sizeof(T) + 2)
+        error("literal must match the result type size");
 
-    return is_simple_zero ? T{} : from_hex<T>(&literal[2]);
+    T r{};
+    internal::from_hex(s, r.bytes);
+    return r;
 }
-}  // namespace internal
 
 /// Literal for evmc::address.
-template <char... c>
-constexpr address operator""_address() noexcept
+constexpr address operator""_address(const char* s) noexcept
 {
-    return internal::from_literal<address, c...>();
+    return to<address>(s);
 }
 
 /// Literal for evmc::bytes32.
-template <char... c>
-constexpr bytes32 operator""_bytes32() noexcept
+constexpr bytes32 operator""_bytes32(const char* s) noexcept
 {
-    return internal::from_literal<bytes32, c...>();
+    return to<bytes32>(s);
 }
 }  // namespace literals
 
diff --git a/include/evmc/hex.hpp b/include/evmc/hex.hpp
index 1a6ee4fec..47cd61413 100644
--- a/include/evmc/hex.hpp
+++ b/include/evmc/hex.hpp
@@ -35,7 +35,7 @@ inline std::string hex(bytes_view bs)
     return str;
 }
 
-namespace internal_hex
+namespace internal
 {
 /// Extracts the nibble value out of a hex digit.
 /// Returns -1 in case of invalid hex degit.
@@ -88,7 +88,7 @@ inline constexpr bool from_hex(std::string_view hex, OutputIt result) noexcept
 
     return b == empty_byte_mark;
 }
-}  // namespace internal_hex
+}  // namespace internal
 
 /// Validates hex encoded string.
 ///
@@ -102,7 +102,7 @@ inline bool validate_hex(std::string_view hex) noexcept
         noop_output_iterator operator++(int) noexcept { return *this; }  // NOLINT(cert-dcl21-cpp)
     };
 
-    return internal_hex::from_hex(hex, noop_output_iterator{});
+    return internal::from_hex(hex, noop_output_iterator{});
 }
 
 /// Decodes hex encoded string to bytes.
@@ -114,7 +114,7 @@ inline std::optional<bytes> from_hex(std::string_view hex)
 {
     bytes bs;
     bs.reserve(hex.size() / 2);
-    if (!internal_hex::from_hex(hex, std::back_inserter(bs)))
+    if (!internal::from_hex(hex, std::back_inserter(bs)))
         return {};
     return bs;
 }