cerc-io/solidity
10
0
Fork 0
mirror of https://github.com/ethereum/solidity synced 2023-10-03 13:03:40 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Improved bitsFromValue implementation.

Browse Source
This commit is contained in:
chriseth 2019-03-25 18:22:15 +01:00
parent 7fea159d27
commit cfe630c717
1 changed files with 11 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
libyul/optimiser/ValueConstraintBasedSimplifier.cpp
View File

@ -180,15 +180,20 @@ ValueConstraint ValueConstraint::valueFromBits(u256 _minBits, u256 _maxBits)
ValueConstraint ValueConstraint::bitsFromValue(u256 _minValue, u256 _maxValue) ValueConstraint ValueConstraint::bitsFromValue(u256 _minValue, u256 _maxValue)
{ {
if (_minValue == _maxValue) // Summary of algorithm: Retain the comon higher order bit prefix between
return constant(_minValue); // _minValue and _maxValue and starting from the point of divergence,
// set all following _maxBits bits to 1, and all following _minBits bits to 0.
int highestBit = highestBitSet(_maxValue); // Reasoning: If we count up from _minValue to _maxValue, then the common upper
// bits will not change.
int divergence = highestBitSet(_minValue ^ _maxValue);
u256 lowerBits = u256(-1) >> (255 - divergence);
u256 minBits = _minValue & (~lowerBits);
u256 maxBits = _maxValue | lowerBits;
return ValueConstraint{ return ValueConstraint{
move(_minValue), move(_minValue),
move(_maxValue), move(_maxValue),
0, move(minBits),
u256(-1) >> (255 - highestBit) move(maxBits)
}; };
} }