The implementation of constant-time swap and select on aarch64 platforms used a cmp instruction in inline assembly to check whether an 8-bit wide selector was 0. The cmp instruction works on 32-bit registers, which included the unspecified high 24 bits of the cmp operand. Depending on the execution environment the cmp could thus potentially return an incorrect result because its operand's high bits in the inline assembly were set when Rust expected them to be unset. This could lead to incorrect results for the constant-time swap and select operations built from this comparison.

In certain circumstances the swap and select instructions on aarch64 platforms returned incorrect results.

Starting from version 0.0.6, the selector is compared using a tst instruction with a mask, which only compares the first 8 bits of the selector.