def c_next

bend-collections-laws-crypto@1.0.0.0 · proofs/crypto/curve25519/limbs.bend:227

import Base
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/nat.bend as N
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend as L
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/word.bend as WD

227def c_next(+one: Nat, +h1: {one == 1n : Nat}, +x: U32, +c: U32, +hx: {Nat.is_le(v(x), WD.sc(28n, one)) == True{} : Bool}, +hc: {Nat.is_le(v(c), WD.sc(21n, one)) == True{} : Bool}) -> {Nat.is_le(v(U32.div(U32.add(x, c), 256)), WD.sc(21n, one)) == True{} : Bool}:
228  +s = U32.add(x, c)
229  +hs = L.subst(Nat, z => {Nat.is_lt(z, WD.sc(29n, one)) == True{} : Bool}, Nat.add(v(x), v(c)), v(s), Equal.sym(Nat, v(s), Nat.add(v(x), v(c)), s_v(one, h1, x, c, hx, hc)), s_lt(one, h1, x, c, hx, hc))
230  N.lt_le(v(U32.div(s, 256)), WD.sc(21n, one), hi_lt(21n, one, h1, s, hs))