feat: add an __RBIT impl for x86_64

Author: g0nz4I0

Inc/MockedDrivers/compiler_specific.hpp

@@ -6,7 +6,29 @@ This file contains implementatios or altername names for
 ARM GCC compiler that don't work in x86_64
 
 */
-#define __RBIT                            
+static inline uint32_t __RBIT(uint32_t val) {
+    // 1. Hardware Byte Swap (Optimization: handles the large movements)
+    // MSVC uses _byteswap_ulong, GCC/Clang uses __builtin_bswap32
+#if defined(_MSC_VER)
+    val = _byteswap_ulong(val);
+#else
+    val = __builtin_bswap32(val);
+#endif
+
+    // 2. Swap Nibbles (within bytes)
+    // 0xF0 = 1111 0000 -> shifts to 0000 1111
+    val = ((val & 0xF0F0F0F0) >> 4) | ((val & 0x0F0F0F0F) << 4);
+
+    // 3. Swap Bit-Pairs (within nibbles)
+    // 0xCC = 1100 1100 -> shifts to 0011 0011
+    val = ((val & 0xCCCCCCCC) >> 2) | ((val & 0x33333333) << 2);
+
+    // 4. Swap Single Bits (within pairs)
+    // 0xAA = 1010 1010 -> shifts to 0101 0101
+    val = ((val & 0xAAAAAAAA) >> 1) | ((val & 0x55555555) << 1);
+
+    return val;
+}                         
 #define __CLZ                             __builtin_clz
 #define __COMPILER_BARRIER()                asm volatile("" ::: "memory")
 #define __DSB()                         __asm__ volatile ("mfence" ::: "memory");