Macro hopper_fast_entrypoint 

macro_rules! hopper_fast_entrypoint {
    ( $process_instruction:expr ) => { ... };
    ( $process_instruction:expr, $maximum:expr ) => { ... };
}

Without the simd-0321 feature the “fast” entrypoint is an alias for the standard scanning entrypoint. The SIMD-0321 gate is live on every public cluster (mainnet-beta 2026-04-01), so the two-argument form is sound to build; it stays opt-in because the r2 path measured CU-neutral against the fused scanning walk for ~368 bytes of extra .text (see the simd-0321 feature note in the workspace Cargo.toml). Build with --features simd-0321 to select the r2 entrypoint.