Merge pull request #44 from Demogorgon314/perf-bt-crc-hotpath

Replace runtime CRC32 table setup with a constexpr lookup table for faster output and feature report checksums

src/utils.h

@@ -2,6 +2,7 @@
 // Created by awalol on 2026/3/4.
 //
 
+#include <array>
 #include <cstdint>
 #include <iomanip>
 #include <iostream>
@@ -89,18 +90,37 @@ inline const char *opcode_to_str(const uint16_t opcode) {
     }
 }
 
-inline uint32_t crc32(const uint8_t* data, size_t size) {
-    uint32_t crc = ~0xEADA2D49;  // 0xA2 seed
+inline constexpr uint32_t crc32_table_entry(uint32_t index) {
+    for (unsigned bit = 0; bit < 8; ++bit) {
+        index = (index >> 1) ^ (0xEDB88320 & -(index & 1));
+    }
+    return index;
+}
+
+inline constexpr auto make_crc32_table() {
+    std::array<uint32_t, 256> table{};
+    for (uint32_t i = 0; i < table.size(); ++i) {
+        table[i] = crc32_table_entry(i);
+    }
+    return table;
+}
+
+inline constexpr auto crc32_lookup_table = make_crc32_table();
+
+inline uint32_t crc32_seeded(const uint8_t *data, size_t size, const uint32_t seed) {
+    uint32_t crc = ~seed;
 
     while (size--) {
-        crc ^= *data++;
-        for (unsigned i = 0; i < 8; i++)
-            crc = ((crc >> 1) ^ (0xEDB88320 & -(crc & 1)));
+        crc = (crc >> 8) ^ crc32_lookup_table[(crc ^ *data++) & 0xff];
     }
 
     return ~crc;
 }
 
+inline uint32_t crc32(const uint8_t* data, size_t size) {
+    return crc32_seeded(data, size, 0xEADA2D49); // 0xA2 seed
+}
+
 inline void fill_output_report_checksum(uint8_t* outputData,size_t len)
 {
     uint32_t crc = crc32(outputData, len - 4);
@@ -112,15 +132,7 @@ inline void fill_output_report_checksum(uint8_t* outputData,size_t len)
 
 inline uint32_t crc32_feature(const uint8_t *data, std::size_t size) {
     // https://github.com/rafaelvaloto/Dualsense-Multiplatform/blob/main/Source/Private/GCore/Utils/CR32.cpp
-    uint32_t crc = ~0x2060efc3; // 0x53 seed
-
-    while (size--) {
-        crc ^= *data++;
-        for (unsigned i = 0; i < 8; i++)
-            crc = ((crc >> 1) ^ (0xEDB88320 & -(crc & 1)));
-    }
-
-    return ~crc;
+    return crc32_seeded(data, size, 0x2060efc3); // 0x53 seed
 }
 
 inline void fill_feature_report_checksum(uint8_t *data, const size_t len) {
@@ -242,4 +254,4 @@ inline void print_hex(const uint8_t* data,size_t size) {
         std::cout << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(data[i]) << " ";
     }
     std::cout << std::endl;
-}
+}