Fast Arrays support initialization of the entire array in just constant time, in addition to supporting constant-time reading and writing of individual elements. Jayanti and Shun introduced concurrent fast arrays, including a generalized fast array which supports constant-time read-modify-write (RMW) operations in addition to reads and writes. Their generalized algorithm, however, assumes mixed-size atomicity—i.e., that 128-bit compare-and-swap and 64-bit read-modify-write operations can be performed concurrently on the same location—which is not available in most programming languages (e.g., C++ and Rust) and not guaranteed on most architectures (e.g., x86 and ARM), as opposed to fixed-size atomicity.