src/crc.bend source

src/crc.bend on the hub · documented module

# src/crc: CRC-32. PNG covers the chunk type and the chunk data with the# ISO 3309 / ITU-T V.42 polynomial (ISO/IEC 15948 / W3C PNG).import Base# the reflected polynomialdef crc.poly() -> U32:  3988292384# eight shifts, one per bit, low bit first. The Nat shrinks, so it is first.def crc.bit(nn: Nat, odd: Bool, +cc: U32) -> U32:  match nn odd:    case 0n _odd:      cc    case 1n+p True{}:      +n1 = ((cc >> 1n : U32) .^. crc.poly() : U32)      crc.bit(p, U32.is_eq((n1 .&. 1 : U32), 1), n1)    case 1n+p False{}:      +n0 = (cc >> 1n : U32)      crc.bit(p, U32.is_eq((n0 .&. 1 : U32), 1), n0)# fold one byte into the registerdef crc.byte(+cc: U32, +bb: U32) -> U32:  +x = (cc .^. bb : U32)  crc.bit(8n, U32.is_eq((x .&. 1 : U32), 1), x)# fold every byte, register still inverted. The list shrinks, so it is first.def crc.fold(xs: List<&2, U32>, +cc: U32) -> U32:  match xs:    case Nil{}:      cc    case Con{+b, t}:      crc.fold(t, crc.byte(cc, b))# CRC-32 of the bytes, init and final xor all onesdef crc32(xs: List<&2, U32>) -> U32:  (crc.fold(xs, 4294967295) .^. 4294967295 : U32)