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Ensure safety of ctz_debruijn implementation. #1194

Merged
merged 1 commit into from
Jan 18, 2023
Merged

Ensure safety of ctz_debruijn implementation. #1194

merged 1 commit into from
Jan 18, 2023

Commits on Jan 17, 2023

  1. Ensure safety of ctz_debruijn implementation. 

    Adding U to the magic constants ensures that we are not mixing unsigned and signed value during multiplication, and ensures that the multiplication will not be subject to integer promotion.

The (uint32_t)/(uint64_t) casts ensure the values are properly truncated no matter the size of an int.

Prior to this commit, if secp256k1_ctz32_var_debruijn were some how managed to be built on a platform with 64-bit ints, (though this function is specifically only intended to be used on 32-bit platforms) it would perform an out-of-bounds array access.
    @roconnor-blockstream
    roconnor-blockstream committed Jan 17, 2023
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