def calculate_block

bend-edit-distance@0.2.2.0 · src/Myers.bend:94

import Base

94# calculateBlock / Advance_Block from Myers. Addition intentionally wraps
95# at 32 bits. Xv uses the original Eq, before the negative carry is added.
96def calculate_block(block: Block, +eq: U32, hin: Carry) -> Block & Carry:
97  Block{+pv, +mv, score} = block
98  Carry{hin_positive, +hin_negative} = hin
99  +xv = U32.or(eq, mv)
100  +eq_in = U32.or(eq, hin_negative)
101  +xh = (U32.xor(U32.add(U32.and(eq_in, pv), pv), pv) .|. eq_in : U32)
102  +ph = U32.or(mv, U32.not(U32.or(xh, pv)))
103  +mh = U32.and(pv, xh)
104  +hout_positive = U32.shrn(ph, 31n)
105  +hout_negative = U32.shrn(mh, 31n)
106  +ph_shifted = U32.or(U32.shl(ph), hin_positive)
107  mh_shifted = U32.or(U32.shl(mh), hin_negative)
108  next_pv = U32.or(mh_shifted, U32.not(U32.or(xv, ph_shifted)))
109  next_mv = U32.and(ph_shifted, xv)
110  (Block{next_pv, next_mv, U32.sub(U32.add(score, hout_positive), hout_negative)},
111    Carry{hout_positive, hout_negative})