From 007641a84bb183f028e20161bf310d5068ef2bd2 Mon Sep 17 00:00:00 2001
From: artur-zawlocki <artur.zawlocki@gmail.com>
Date: Thu, 30 Oct 2014 12:56:52 +0000
Subject: [PATCH] SIGEXTEND: first try [#81700414]

---
 libevmjit/Compiler.cpp | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/libevmjit/Compiler.cpp b/libevmjit/Compiler.cpp
index 8dc19e84c..ea74d1051 100644
--- a/libevmjit/Compiler.cpp
+++ b/libevmjit/Compiler.cpp
@@ -372,14 +372,14 @@ void Compiler::compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode,
 			break;
 		}
 
-		/*case Instruction::NEG:
+		case Instruction::BNOT:
 		{
 			auto top = stack.pop();
-			auto zero = Constant::get(0);
-			auto res = m_builder.CreateSub(zero, top);
+			auto allones = llvm::ConstantInt::get(Type::i256, llvm::APInt::getAllOnesValue(256));
+			auto res = m_builder.CreateXor(top, allones);
 			stack.push(res);
 			break;
-		}*/
+		}
 
 		case Instruction::LT:
 		{
@@ -505,6 +505,35 @@ void Compiler::compileBasicBlock(BasicBlock& basicBlock, bytesConstRef bytecode,
 			break;
 		}
 
+		case Instruction::SIGNEXTEND:
+		{
+			auto k = stack.pop();
+			auto b = stack.pop();
+			auto k32 = m_builder.CreateTrunc(k, m_builder.getIntNTy(5), "k_32");
+			auto k32ext = m_builder.CreateZExt(k32, Type::i256);
+			auto k32x8 = m_builder.CreateMul(k32ext, Constant::get(8), "kx8");
+
+			// test for b >> (k * 8 + 7)
+			auto val = m_builder.CreateAdd(k32x8, llvm::ConstantInt::get(Type::i256, 7));
+			auto tmp = m_builder.CreateAShr(b, val);
+			auto bitset = m_builder.CreateTrunc(tmp, m_builder.getInt1Ty());
+
+			// shift left by (31 - k) * 8 = (248 - k*8), then do arithmetic shr by the same amount.
+			auto shiftSize = m_builder.CreateSub(llvm::ConstantInt::get(Type::i256, 31 * 8), k32x8);
+			auto bshl = m_builder.CreateShl(b, shiftSize);
+			auto bshr = m_builder.CreateAShr(bshl, shiftSize);
+
+			// bshr is our final value if 0 <= k <= 30 and bitset is true,
+			// otherwise we push back b unchanged
+			auto kInRange = m_builder.CreateICmpULE(k, llvm::ConstantInt::get(Type::i256, 30));
+			auto cond = m_builder.CreateAnd(kInRange, bitset);
+
+			auto result = m_builder.CreateSelect(cond, bshr, b);
+			stack.push(result);
+
+			break;
+		}
+
 		case Instruction::SHA3:
 		{
 			auto inOff = stack.pop();