X25519.mask_last: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/spec/crypto/curve25519/x25519.bend as X25519
Lines 40-50 of bend-collections-laws-crypto@1.0.0.0/spec/crypto/curve25519/x25519.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/curve25519/x25519.bend&start_line=40&end_line=50

import Base

# decodeUCoordinate: the last byte's top bit masked (bits = 255)
def mask_last(xs: List<&2, U32>) -> List<&2, U32>:
  match xs:
    case Nil{}:
      Nil{}
    case Con{x, xt}:
      match xt:
        case Nil{}:
          Con{U32.and(x, 127), Nil{}}
        case Con{y, yt}:
          Con{x, mask_last(Con{y, yt})}

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.and