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Merge pull request #4277 from ethereum/signedRightShift

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Signed Right Shift: Additional test and more explanation.
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Daniel Kirchner 2018-06-12 17:19:20 +02:00 committed by GitHub
commit e2f4a9fcf4
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2 changed files with 40 additions and 2 deletions
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9
libsolidity/ast/Types.cpp
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@ -1088,8 +1088,13 @@ TypePointer RationalNumberType::binaryOperatorResult(Token::Value _operator, Typ
else
{
if (m_value.numerator() < 0)
// add 1 to the negative value before dividing to get a result that is strictly too large
// subtract 1 afterwards to round towards negative infinity
// Add 1 to the negative value before dividing to get a result that is strictly too large,
// then subtract 1 afterwards to round towards negative infinity.
// This is the same algorithm as used in ExpressionCompiler::appendShiftOperatorCode(...).
// To see this note that for negative x, xor(x,all_ones) = (-x-1) and
// therefore xor(div(xor(x,all_ones), exp(2, shift_amount)), all_ones) is
// -(-x - 1) / 2^shift_amount - 1, which is the same as
// (x + 1) / 2^shift_amount - 1.
value = rational((m_value.numerator() + 1) / boost::multiprecision::pow(bigint(2), exponent) - bigint(1), 1);
else
value = rational(m_value.numerator() / boost::multiprecision::pow(bigint(2), exponent), 1);

33
test/libsolidity/SolidityEndToEndTest.cpp
View File

@ -10508,6 +10508,39 @@ BOOST_AUTO_TEST_CASE(shift_right_garbled)
ABI_CHECK(callContractFunction("f(uint8,uint8)", u256(0x0), u256(0x1004)), encodeArgs(u256(0xf)));
}
BOOST_AUTO_TEST_CASE(shift_right_garbled_signed)
{
char const* sourceCode = R"(
contract C {
function f(int8 a, uint8 b) returns (int) {
assembly {
a := 0xfffffff0
}
// Higher bits should be signextended before the shift
return a >> b;
}
function g(int8 a, uint8 b) returns (int) {
assembly {
a := 0xf0
}
// Higher bits should be signextended before the shift
return a >> b;
}
}
)";
compileAndRun(sourceCode, 0, "C");
ABI_CHECK(callContractFunction("f(int8,uint8)", u256(0x0), u256(3)), encodeArgs(u256(-2)));
ABI_CHECK(callContractFunction("f(int8,uint8)", u256(0x0), u256(4)), encodeArgs(u256(-1)));
ABI_CHECK(callContractFunction("f(int8,uint8)", u256(0x0), u256(0xFF)), encodeArgs(u256(-1)));
ABI_CHECK(callContractFunction("f(int8,uint8)", u256(0x0), u256(0x1003)), encodeArgs(u256(-2)));
ABI_CHECK(callContractFunction("f(int8,uint8)", u256(0x0), u256(0x1004)), encodeArgs(u256(-1)));
ABI_CHECK(callContractFunction("g(int8,uint8)", u256(0x0), u256(3)), encodeArgs(u256(-2)));
ABI_CHECK(callContractFunction("g(int8,uint8)", u256(0x0), u256(4)), encodeArgs(u256(-1)));
ABI_CHECK(callContractFunction("g(int8,uint8)", u256(0x0), u256(0xFF)), encodeArgs(u256(-1)));
ABI_CHECK(callContractFunction("g(int8,uint8)", u256(0x0), u256(0x1003)), encodeArgs(u256(-2)));
ABI_CHECK(callContractFunction("g(int8,uint8)", u256(0x0), u256(0x1004)), encodeArgs(u256(-1)));
}
BOOST_AUTO_TEST_CASE(shift_right_uint32)
{
char const* sourceCode = R"(