Point.dec_y: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend as Point
Lines 156-168 of bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend&start_line=156&end_line=168

import Base
import bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend as F

def dec_y(+c: Cs, +y: List<&2, U32>, +x0: U32, bad: Bool) -> Maybe<&2, Pt>:
  match bad:
    case True{}:
      None{}
    case False{}:
      +yy = F.sq(y)
      +u = F.sub(yy, F.one())
      +v = F.add(F.mul(cs_d(c), yy), F.one())
      +v3 = F.mul(F.sq(v), v)
      +v7 = F.mul(F.sq(v3), v)
      +x = F.mul(F.mul(u, v3), F.pow_p58(F.mul(u, v7)))
      +vxx = F.mul(v, F.sq(x))
      dec_root(c, x, y, x0, u, vxx, F.eq(vxx, u), F.eq(vxx, F.neg(u)))

Uses (16):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=add
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=eq
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=mul
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=neg
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=one
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=pow_p58
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=sq
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/curve25519/field.bend&name=sub
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend&name=Cs
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend&name=Pt
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend&name=cs_d
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/ed25519/point.bend&name=dec_root