Merge pull request #9479 from ethereum/exp

Implement checked exponentiation.

libsolidity/codegen/YulUtilFunctions.cpp

@@ -597,6 +597,139 @@ string YulUtilFunctions::overflowCheckedIntSubFunction(IntegerType const& _type)
 	});
 }
 
+string YulUtilFunctions::overflowCheckedIntExpFunction(
+	IntegerType const& _type,
+	IntegerType const& _exponentType
+)
+{
+	solAssert(!_exponentType.isSigned(), "");
+
+	string functionName = "checked_exp_" + _type.identifier() + "_" + _exponentType.identifier();
+	return m_functionCollector.createFunction(functionName, [&]() {
+		return
+			Whiskers(R"(
+			function <functionName>(base, exponent) -> power {
+				base := <baseCleanupFunction>(base)
+				exponent := <exponentCleanupFunction>(exponent)
+				<?signed>
+					power := <exp>(base, exponent, <minValue>, <maxValue>)
+				<!signed>
+					power := <exp>(base, exponent, <maxValue>)
+				</signed>
+
+			}
+			)")
+			("functionName", functionName)
+			("signed", _type.isSigned())
+			("exp", _type.isSigned() ? overflowCheckedSignedExpFunction() : overflowCheckedUnsignedExpFunction())
+			("maxValue", toCompactHexWithPrefix(_type.max()))
+			("minValue", toCompactHexWithPrefix(_type.min()))
+			("baseCleanupFunction", cleanupFunction(_type))
+			("exponentCleanupFunction", cleanupFunction(_exponentType))
+			.render();
+	});
+}
+
+string YulUtilFunctions::overflowCheckedUnsignedExpFunction()
+{
+	string functionName = "checked_exp_unsigned";
+	return m_functionCollector.createFunction(functionName, [&]() {
+		return
+			Whiskers(R"(
+			function <functionName>(base, exponent, max) -> power {
+				// This function currently cannot be inlined because of the
+				// "leave" statements. We have to improve the optimizer.
+
+				// Note that 0**0 == 1
+				if iszero(exponent) { power := 1 leave }
+				if iszero(base) { power := 0 leave }
+
+				power := 1
+
+				for { } gt(exponent, 1) {}
+				{
+					// overflow check for base * base
+					if gt(base, div(max, base)) { revert(0, 0) }
+					if and(exponent, 1)
+					{
+						// no check needed here because base >= power
+						power := mul(power, base)
+					}
+					base := mul(base, base)
+					exponent := <shr_1>(exponent)
+				}
+				if gt(power, div(max, base)) { revert(0, 0) }
+				power := mul(power, base)
+			}
+			)")
+			("functionName", functionName)
+			("shr_1", shiftRightFunction(1))
+			.render();
+	});
+}
+
+string YulUtilFunctions::overflowCheckedSignedExpFunction()
+{
+	string functionName = "checked_exp_signed";
+	return m_functionCollector.createFunction(functionName, [&]() {
+		return
+			Whiskers(R"(
+			function <functionName>(base, exponent, min, max) -> power {
+				// Currently, `leave` avoids this function being inlined.
+				// We have to improve the optimizer.
+
+				// Note that 0**0 == 1
+				switch exponent
+				case 0 { power := 1 leave }
+				case 1 { power := base leave }
+				if iszero(base) { power := 0 leave }
+
+				power := 1
+
+				// We pull out the first iteration because it is the only one in which
+				// base can be negative.
+				// Exponent is at least 2 here.
+
+				// overflow check for base * base
+				switch sgt(base, 0)
+				case 1 { if gt(base, div(max, base)) { revert(0, 0) } }
+				case 0 { if slt(base, sdiv(max, base)) { revert(0, 0) } }
+				if and(exponent, 1)
+				{
+					power := base
+				}
+				base := mul(base, base)
+				exponent := <shr_1>(exponent)
+
+				// Below this point, base is always positive.
+
+				for { } gt(exponent, 1) {}
+				{
+					// overflow check for base * base
+					if gt(base, div(max, base)) { revert(0, 0) }
+					if and(exponent, 1)
+					{
+						// No checks for power := mul(power, base) needed, because the check
+						// for base * base above is sufficient, since:
+						// |power| <= base (proof by induction) and thus:
+						// |power * base| <= base * base <= max <= |min|
+						power := mul(power, base)
+					}
+					base := mul(base, base)
+					exponent := <shr_1>(exponent)
+				}
+
+				if and(sgt(power, 0), gt(power, div(max, base))) { revert(0, 0) }
+				if and(slt(power, 0), slt(power, sdiv(min, base))) { revert(0, 0) }
+				power := mul(power, base)
+			}
+			)")
+			("functionName", functionName)
+			("shr_1", shiftRightFunction(1))
+			.render();
+	});
+}
+
 string YulUtilFunctions::extractByteArrayLengthFunction()
 {
 	string functionName = "extract_byte_array_length";

libsolidity/codegen/YulUtilFunctions.h

@@ -125,6 +125,21 @@ public:
 	/// signature: (x, y) -> diff
 	std::string overflowCheckedIntSubFunction(IntegerType const& _type);
 
+	/// @returns the name of the exponentiation function.
+	/// signature: (base, exponent) -> power
+	std::string overflowCheckedIntExpFunction(IntegerType const& _type, IntegerType const& _exponentType);
+
+	/// Generic unsigned checked exponentiation function.
+	/// Reverts if the result is larger than max.
+	/// signature: (base, exponent, max) -> power
+	std::string overflowCheckedUnsignedExpFunction();
+
+	/// Generic signed checked exponentiation function.
+	/// Reverts if the result is smaller than min or larger than max.
+	/// The code relies on max <= |min| and min < 0.
+	/// signature: (base, exponent, min, max) -> power
+	std::string overflowCheckedSignedExpFunction();
+
 	/// @returns the name of a function that fetches the length of the given
 	/// array
 	/// signature: (array) -> length

libsolidity/codegen/ir/IRGeneratorForStatements.cpp

@@ -277,6 +277,7 @@ bool IRGeneratorForStatements::visit(Assignment const& _assignment)
 		solAssert(type(_assignment.leftHandSide()).isValueType(), "Compound operators only available for value types.");
 		solAssert(rightIntermediateType->isValueType(), "Compound operators only available for value types.");
 		IRVariable leftIntermediate = readFromLValue(*m_currentLValue);
+		solAssert(binaryOperator != Token::Exp, "");
 		if (TokenTraits::isShiftOp(binaryOperator))
 		{
 			solAssert(type(_assignment) == leftIntermediate.type(), "");
@@ -593,11 +594,17 @@ bool IRGeneratorForStatements::visit(BinaryOperation const& _binOp)
 			solAssert(false, "Unknown comparison operator.");
 		define(_binOp) << expr << "\n";
 	}
-	else if (TokenTraits::isShiftOp(op))
+	else if (TokenTraits::isShiftOp(op) || op == Token::Exp)
 	{
 		IRVariable left = convert(_binOp.leftExpression(), *commonType);
 		IRVariable right = convert(_binOp.rightExpression(), *type(_binOp.rightExpression()).mobileType());
-		define(_binOp) << shiftOperation(_binOp.getOperator(), left, right) << "\n";
+		if (op == Token::Exp)
+			define(_binOp) << m_utils.overflowCheckedIntExpFunction(
+				dynamic_cast<IntegerType const&>(left.type()),
+				dynamic_cast<IntegerType const&>(right.type())
+			) << "(" << left.name() << ", " << right.name() << ")\n";
+		else
+			define(_binOp) << shiftOperation(_binOp.getOperator(), left, right) << "\n";
 	}
 	else
 	{

test/libsolidity/semanticTests/exponentiation/signed_base.sol

@@ -10,5 +10,7 @@ contract test {
         return (x**y1, x**y2);
     }
 }
+// ====
+// compileViaYul: also
 // ----
 // f() -> 9, -27

test/libsolidity/semanticTests/viaYul/exp.sol

@@ -0,0 +1,19 @@
+contract C {
+    function f(uint x, uint y) public returns (uint) {
+        return x**y;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f(uint256,uint256): 0, 0 -> 1
+// f(uint256,uint256): 0, 1 -> 0x00
+// f(uint256,uint256): 0, 2 -> 0x00
+// f(uint256,uint256): 1, 0 -> 1
+// f(uint256,uint256): 1, 1 -> 1
+// f(uint256,uint256): 1, 2 -> 1
+// f(uint256,uint256): 2, 0 -> 1
+// f(uint256,uint256): 2, 1 -> 2
+// f(uint256,uint256): 2, 2 -> 4
+// f(uint256,uint256): 7, 63 -> 174251498233690814305510551794710260107945042018748343
+// f(uint256,uint256): 128, 2 -> 0x4000

test/libsolidity/semanticTests/viaYul/exp_neg.sol

@@ -0,0 +1,28 @@
+contract C {
+    function f(int x, uint y) public returns (int) {
+        return x**y;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f(int256,uint256): 0, 0 -> 1
+// f(int256,uint256): 0, 1 -> 0x00
+// f(int256,uint256): 0, 2 -> 0x00
+// f(int256,uint256): 1, 0 -> 1
+// f(int256,uint256): 1, 1 -> 1
+// f(int256,uint256): 1, 2 -> 1
+// f(int256,uint256): 2, 0 -> 1
+// f(int256,uint256): 2, 1 -> 2
+// f(int256,uint256): 2, 2 -> 4
+// f(int256,uint256): 7, 63 -> 174251498233690814305510551794710260107945042018748343
+// f(int256,uint256): 128, 2 -> 0x4000
+// f(int256,uint256): -1, 0 -> 1
+// f(int256,uint256): -1, 1 -> -1
+// f(int256,uint256): -1, 2 -> 1
+// f(int256,uint256): -2, 0 -> 1
+// f(int256,uint256): -2, 1 -> -2
+// f(int256,uint256): -2, 2 -> 4
+// f(int256,uint256): -7, 63 -> -174251498233690814305510551794710260107945042018748343
+// f(int256,uint256): -128, 2 -> 0x4000
+// f(int256,uint256): -1, 115792089237316195423570985008687907853269984665640564039457584007913129639935 -> -1

test/libsolidity/semanticTests/viaYul/exp_neg_overflow.sol

@@ -0,0 +1,38 @@
+contract C {
+    function f(int8 x, uint y) public returns (int) {
+        return x**y;
+    }
+    function g(int256 x, uint y) public returns (int) {
+        return x**y;
+    }
+}
+// ====
+// compileViaYul: true
+// ----
+// f(int8,uint256): 2, 6 -> 64
+// f(int8,uint256): 2, 7 -> FAILURE
+// f(int8,uint256): 2, 8 -> FAILURE
+// f(int8,uint256): -2, 6 -> 64
+// f(int8,uint256): -2, 7 -> -128
+// f(int8,uint256): -2, 8 -> FAILURE
+// f(int8,uint256): 6, 3 -> FAILURE
+// f(int8,uint256): 7, 2 -> 0x31
+// f(int8,uint256): 7, 3 -> FAILURE
+// f(int8,uint256): -7, 2 -> 0x31
+// f(int8,uint256): -7, 3 -> FAILURE
+// f(int8,uint256): -7, 4 -> FAILURE
+// f(int8,uint256): 127, 31 -> FAILURE
+// f(int8,uint256): 127, 131 -> FAILURE
+// f(int8,uint256): -128, 0 -> 1
+// f(int8,uint256): -128, 1 -> -128
+// f(int8,uint256): -128, 31 -> FAILURE
+// f(int8,uint256): -128, 131 -> FAILURE
+// f(int8,uint256): -11, 2 -> 121
+// f(int8,uint256): -12, 2 -> FAILURE
+// f(int8,uint256): 12, 2 -> FAILURE
+// f(int8,uint256): -5, 3 -> -125
+// f(int8,uint256): -6, 3 -> FAILURE
+// g(int256,uint256): -7, 90 -> 11450477594321044359340126713545146077054004823284978858214566372120240027249
+// g(int256,uint256): -7, 91 -> FAILURE
+// g(int256,uint256): -63, 42 -> 3735107253208426854890677539053540390278853997836851167913009474475553834369
+// g(int256,uint256): -63, 43 -> FAILURE

test/libsolidity/semanticTests/viaYul/exp_overflow.sol

@@ -0,0 +1,31 @@
+contract C {
+    function f(uint8 x, uint8 y) public returns (uint) {
+        return x**y;
+    }
+    function g(uint x, uint y) public returns (uint) {
+        return x**y;
+    }
+}
+// ====
+// compileViaYul: true
+// ----
+// f(uint8,uint8): 2, 7 -> 0x80
+// f(uint8,uint8): 2, 8 -> FAILURE
+// f(uint8,uint8): 15, 2 -> 225
+// f(uint8,uint8): 6, 3 -> 0xd8
+// f(uint8,uint8): 7, 2 -> 0x31
+// f(uint8,uint8): 7, 3 -> FAILURE
+// f(uint8,uint8): 7, 4 -> FAILURE
+// f(uint8,uint8): 255, 31 -> FAILURE
+// f(uint8,uint8): 255, 131 -> FAILURE
+// g(uint256,uint256): 0x200000000000000000000000000000000, 1 -> 0x0200000000000000000000000000000000
+// g(uint256,uint256): 0x100000000000000000000000000000010, 2 -> FAILURE
+// g(uint256,uint256): 0x200000000000000000000000000000000, 2 -> FAILURE
+// g(uint256,uint256): 0x200000000000000000000000000000000, 3 -> FAILURE
+// g(uint256,uint256): 255, 31 -> 400631961586894742455537928461950192806830589109049416147172451019287109375
+// g(uint256,uint256): 255, 32 -> -13630939032658036097408813250890608687528184442832962921928608997994916749311
+// g(uint256,uint256): 255, 33 -> FAILURE
+// g(uint256,uint256): 255, 131 -> FAILURE
+// g(uint256,uint256): 258, 31 -> 575719427506838823084316385994930914701079543089399988096291424922125729792
+// g(uint256,uint256): 258, 37 -> FAILURE
+// g(uint256,uint256): 258, 131 -> FAILURE

test/libsolidity/semanticTests/viaYul/exp_various.sol

@@ -0,0 +1,50 @@
+contract C {
+    function f(uint8 x, uint8 y) public returns (uint) {
+        return x**y;
+    }
+    function g(uint x, uint y) public returns (uint) {
+        return x**y;
+    }
+}
+// ====
+// compileViaYul: also
+// ----
+// f(uint8,uint8): 0, 0 -> 1
+// f(uint8,uint8): 0, 1 -> 0x00
+// f(uint8,uint8): 0, 2 -> 0x00
+// f(uint8,uint8): 0, 3 -> 0x00
+// f(uint8,uint8): 1, 0 -> 1
+// f(uint8,uint8): 1, 1 -> 1
+// f(uint8,uint8): 1, 2 -> 1
+// f(uint8,uint8): 1, 3 -> 1
+// f(uint8,uint8): 2, 0 -> 1
+// f(uint8,uint8): 2, 1 -> 2
+// f(uint8,uint8): 2, 2 -> 4
+// f(uint8,uint8): 2, 3 -> 8
+// f(uint8,uint8): 3, 0 -> 1
+// f(uint8,uint8): 3, 1 -> 3
+// f(uint8,uint8): 3, 2 -> 9
+// f(uint8,uint8): 3, 3 -> 0x1b
+// f(uint8,uint8): 10, 0 -> 1
+// f(uint8,uint8): 10, 1 -> 0x0a
+// f(uint8,uint8): 10, 2 -> 100
+// g(uint256,uint256): 0, 0 -> 1
+// g(uint256,uint256): 0, 1 -> 0x00
+// g(uint256,uint256): 0, 2 -> 0x00
+// g(uint256,uint256): 0, 3 -> 0x00
+// g(uint256,uint256): 1, 0 -> 1
+// g(uint256,uint256): 1, 1 -> 1
+// g(uint256,uint256): 1, 2 -> 1
+// g(uint256,uint256): 1, 3 -> 1
+// g(uint256,uint256): 2, 0 -> 1
+// g(uint256,uint256): 2, 1 -> 2
+// g(uint256,uint256): 2, 2 -> 4
+// g(uint256,uint256): 2, 3 -> 8
+// g(uint256,uint256): 3, 0 -> 1
+// g(uint256,uint256): 3, 1 -> 3
+// g(uint256,uint256): 3, 2 -> 9
+// g(uint256,uint256): 3, 3 -> 0x1b
+// g(uint256,uint256): 10, 10 -> 10000000000
+// g(uint256,uint256): 10, 77 -> -15792089237316195423570985008687907853269984665640564039457584007913129639936
+// g(uint256,uint256): 256, 2 -> 0x010000
+// g(uint256,uint256): 256, 31 -> 0x0100000000000000000000000000000000000000000000000000000000000000