thumb32: Implement RBIT

src/frontend/A32/decoder/thumb32.h

@@ -281,7 +281,7 @@ std::optional<std::reference_wrapper<const Thumb32Matcher<V>>> DecodeThumb32(u32
         //INST(&V::thumb32_QDSUB,          "QDSUB",                    "111110101000----1111----1011----"),
         //INST(&V::thumb32_REV,            "REV",                      "111110101001----1111----1000----"),
         //INST(&V::thumb32_REV16,          "REV16",                    "111110101001----1111----1001----"),
-        //INST(&V::thumb32_RBIT,           "RBIT",                     "111110101001----1111----1010----"),
+        INST(&V::thumb32_RBIT,           "RBIT",                     "111110101001nnnn1111dddd1010mmmm"),
         INST(&V::thumb32_REVSH,          "REVSH",                    "111110101001nnnn1111dddd1011mmmm"),
         INST(&V::thumb32_SEL,            "SEL",                      "111110101010nnnn1111dddd1000mmmm"),
         INST(&V::thumb32_CLZ,            "CLZ",                      "111110101011nnnn1111dddd1000mmmm"),

src/frontend/A32/translate/impl/thumb32_misc.cpp

@@ -19,6 +19,31 @@ bool ThumbTranslatorVisitor::thumb32_CLZ(Reg n, Reg d, Reg m) {
     return true;
 }
 
+bool ThumbTranslatorVisitor::thumb32_RBIT(Reg n, Reg d, Reg m) {
+    if (m != n || d == Reg::PC || m == Reg::PC) {
+        return UnpredictableInstruction();
+    }
+
+    const IR::U32 swapped = ir.ByteReverseWord(ir.GetRegister(m));
+
+    // ((x & 0xF0F0F0F0) >> 4) | ((x & 0x0F0F0F0F) << 4)
+    const IR::U32 first_lsr = ir.LogicalShiftRight(ir.And(swapped, ir.Imm32(0xF0F0F0F0)), ir.Imm8(4));
+    const IR::U32 first_lsl = ir.LogicalShiftLeft(ir.And(swapped, ir.Imm32(0x0F0F0F0F)), ir.Imm8(4));
+    const IR::U32 corrected = ir.Or(first_lsl, first_lsr);
+
+    // ((x & 0x88888888) >> 3) | ((x & 0x44444444) >> 1) |
+    // ((x & 0x22222222) << 1) | ((x & 0x11111111) << 3)
+    const IR::U32 second_lsr = ir.LogicalShiftRight(ir.And(corrected, ir.Imm32(0x88888888)), ir.Imm8(3));
+    const IR::U32 third_lsr = ir.LogicalShiftRight(ir.And(corrected, ir.Imm32(0x44444444)), ir.Imm8(1));
+    const IR::U32 second_lsl = ir.LogicalShiftLeft(ir.And(corrected, ir.Imm32(0x22222222)), ir.Imm8(1));
+    const IR::U32 third_lsl = ir.LogicalShiftLeft(ir.And(corrected, ir.Imm32(0x11111111)), ir.Imm8(3));
+
+    const IR::U32 result = ir.Or(ir.Or(ir.Or(second_lsr, third_lsr), second_lsl), third_lsl);
+
+    ir.SetRegister(d, result);
+    return true;
+}
+
 bool ThumbTranslatorVisitor::thumb32_REVSH(Reg n, Reg d, Reg m) {
     if (m != n || d == Reg::PC || m == Reg::PC) {
         return UnpredictableInstruction();

src/frontend/A32/translate/impl/translate_thumb.h

@@ -118,6 +118,7 @@ struct ThumbTranslatorVisitor final {
 
     // thumb32 miscellaneous instructions
     bool thumb32_CLZ(Reg n, Reg d, Reg m);
+    bool thumb32_RBIT(Reg n, Reg d, Reg m);
     bool thumb32_REVSH(Reg n, Reg d, Reg m);
     bool thumb32_SEL(Reg n, Reg d, Reg m);
 };

tests/A32/fuzz_thumb.cpp

@@ -369,6 +369,13 @@ TEST_CASE("Fuzz Thumb32 instructions set", "[JitX64][Thumb][Thumb32]") {
                          const auto n = Common::Bits<16, 19>(inst);
                          return m == n && d != 15 && m != 15;
                      }),
+        ThumbInstGen("111110101001nnnn1111dddd1010mmmm", // RBIT
+                     [](u32 inst) {
+                         const auto d = Common::Bits<8, 11>(inst);
+                         const auto m = Common::Bits<0, 3>(inst);
+                         const auto n = Common::Bits<16, 19>(inst);
+                         return m == n && d != 15 && m != 15;
+                     }),
         ThumbInstGen("111110101001nnnn1111dddd1011mmmm", // REVSH
                      [](u32 inst) {
                          const auto d = Common::Bits<8, 11>(inst);