update: perf CommonCode string decoding

src/core/benchmark/codec.cc

@@ -261,14 +261,14 @@ static void IsMirrorCompare(benchmark::State &state) {
 }
 
 // BENCHMARK(CommonCodeSerialize)->Range(8, 256);
-// BENCHMARK(CommonCodeDeserialize)->Range(8, 256);
+BENCHMARK(CommonCodeDeserialize)->Range(8, 256);
 // BENCHMARK(CommonCodeSerializeShorten)->Range(8, 256);
 // BENCHMARK(CommonCodeDeserializeShorten)->Range(8, 256);
 
 // BENCHMARK(ShortCodeSerialize)->Range(8, 256);
 // BENCHMARK(ShortCodeDeserialize)->Range(8, 256);
 
-BENCHMARK(IsMirrorCompare);
+// BENCHMARK(IsMirrorCompare);
 
 // BENCHMARK(ShortCodeToCommonCode);
 // BENCHMARK(CommonCodeToShortCode);

src/core/common_code/internal/serialize.cc

@@ -4,13 +4,55 @@ namespace klotski::codec {
 
 /// Convert a single hexadecimal digit to a character.
 static char to_hex_char(const uint64_t hex_bit) {
-    [[assume(hex_bit < 0x10)]];
+    KLSK_ASSUME(hex_bit < 0x10);
     if (hex_bit < 0xA) {
         return static_cast<char>(hex_bit + '0');
     }
     return static_cast<char>(hex_bit + 'A' - 10);
 }
 
+constexpr auto CONVERT_TABLE = std::to_array<char>({
+    /// -1 * 48
+    -1, -1, -1, -1, -1, -1,       // [0, 5]
+    -1, -1, -1, -1, -1, -1, -1,   // [6, 12]
+    -1, -1, -1, -1, -1, -1, -1,   // [13, 19]
+    -1, -1, -1, -1, -1, -1, -1,   // [20, 26]
+    -1, -1, -1, -1, -1, -1, -1,   // [27, 33]
+    -1, -1, -1, -1, -1, -1, -1,   // [34, 40]
+    -1, -1, -1, -1, -1, -1, -1,   // [41, 47]
+
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, // [48, 57]
+
+    /// -1 * 7
+    -1, -1, -1, -1, -1, -1, -1,   // [58, 64]
+
+    10, 11, 12, 13, 14, 15,       // [65, 70]
+
+    /// -1 * 26
+    -1, -1, -1, -1, -1, -1, -1,   // [71, 77]
+    -1, -1, -1, -1, -1, -1, -1,   // [78, 84]
+    -1, -1, -1, -1, -1, -1, -1,   // [85, 91]
+    -1, -1, -1, -1, -1,           // [92, 96]
+
+    10, 11, 12, 13, 14, 15,       // [97, 102]
+
+    /// -1 * 25
+    -1, -1, -1, -1, -1, -1, -1,   // [103, 109]
+    -1, -1, -1, -1, -1, -1, -1,   // [110, 116]
+    -1, -1, -1, -1, -1, -1, -1,   // [117, 123]
+    -1, -1, -1, -1,               // [124, 127]
+
+    /// -1 * 128
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
+});
+
 std::string CommonCode::string_encode(uint64_t common_code) {
     char code_str[9];
     for (int i = 0; i < 9; ++i) {
@@ -29,25 +71,19 @@ std::string CommonCode::string_encode_shorten(const uint64_t common_code) {
     return code;
 }
 
-// TODO: direct table lookup can bring about a 30% improvement,
-// TODO:   but it is necessary to confirm the performance of different CPU caches.
 std::optional<uint64_t> CommonCode::string_decode(const std::string_view common_code) {
     if (common_code.length() > 9 || common_code.empty()) {
         return std::nullopt; // invalid string length
     }
-    uint64_t result = 0;
-    for (const auto hex_bit : common_code) {
-        if (hex_bit >= '0' && hex_bit <= '9') { // 0 ~ 9
-            (result <<= 4) |= (hex_bit - '0');
-        } else if (hex_bit >= 'A' && hex_bit <= 'F') { // A ~ F
-            (result <<= 4) |= (hex_bit - 'A' + 10);
-        } else if (hex_bit >= 'a' && hex_bit <= 'f') { // a ~ f
-            (result <<= 4) |= (hex_bit - 'a' + 10);
-        } else {
-            return std::nullopt; // invalid character
+    uint64_t code = 0;
+    for (const uint8_t hex_bit : common_code) {
+        const auto val = CONVERT_TABLE[hex_bit]; // table convert
+        if (val == -1) {
+            return std::nullopt;
         }
+        (code <<= 4) |= val;
     }
-    return result << (36 - common_code.length() * 4); // low-bits fill with zero
+    return code << (36 - common_code.length() * 4); // low-bits fill with zero
 }
 
 } // namespace klotski::codec