Double shift size overflow.md

85 - Double shift size overflow

Double bitwise shifts by large constants whose sum overflows 256 bits can result in unexpected values. Nested logical shift operations whose total shift size is 2**256 or more are incorrectly optimized. This only applies to shifts by numbers of bits that are compile-time constant expressions. This happens when the optimizer is used and evmVersion >= Constantinople. This is due to a compiler bug introduced in v0.5.5 and fixed in v0.5.6. (see here)

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Slide Screenshot

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Slide Text

• Double Shift Size Overflow
• Optimizer Double Bitwise Shifts
• Shift > 2**256 -> Overflow
• Compiler Bug -> Fixed
• solc 0.5.5 -> 0.5.6

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References

• Youtube Reference

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