eip-7939: implement the CLZ opcode #2825
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ehildenb
reviewed
Dec 15, 2025
Co-authored-by: Everett Hildenbrandt <everett.hildenbrandt@gmail.com>
ehildenb
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Dec 15, 2025
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blocked on: #2823
Implementing the CLZ (Counting Leading Zeros) opcode introduced in EIP-7939.
The opcode returns the number of leading zeros in an evm word. There is a special case for 0, in which the returned value is 256. It has a gas cost of five, similar to the other
Wlowopcodes, and is available from the Osaka schedule onwards.To compute the number of leading zeros of a number, we use the
log2IntK builtin, as it returns the index of the highest set bit, which we then subtract from 255.