Function proc_par_blocks 

pub(super) unsafe fn proc_par_blocks(
    key: &ExpandedKey,
    acc: FieldElement,
    par_blocks: &ParBlocks,
) -> FieldElement

Process 4 blocks with R/F algorithm and aggregated reduction

Uses 16 CLMULs for multiplication (4 per block) + 1 CLMUL for reduction = 17 CLMULs total