def hi_mul

bend-collections-laws-crypto@1.0.0.0 · proofs/crypto/argon2/index.bend:171

import Base
import bend-collections-laws-crypto@1.0.0.0/spec/lib/common.bend as C
import bend-collections-laws-crypto@1.0.0.0/spec/math/w64.bend as SW
import bend-collections-laws-crypto@1.0.0.0/src/math/w64.bend as X
import bend-collections-laws-crypto@1.0.0.0/src/math/u64.bend as WU
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/math/typed/w64mul.bend as W64M
import bend-collections-laws-crypto@1.0.0.0/proofs/crypto/argon2/words.bend as LW
import bend-collections-laws-crypto@1.0.0.0/proofs/crypto/argon2/gb.bend as GB

171# The high word of mul32(a, b) is a * b div 2^32.
172def hi_mul(+a: U32, +b: U32) -> {U32.to_nat(X.hi(X.mul32(a, b))) == C.high(32n, Nat.mul(U32.to_nat(a), U32.to_nat(b))) : Nat}:
173  +n = Nat.mul(U32.to_nat(a), U32.to_nat(b))
174  +f64 = L.subst(Nat, z => {C.fits(64n, z) == True{} : Bool}, SW.value(X.mul32(a, b)), n, W64M.mul32_value(a, b), fits_value(X.mul32(a, b)))
175  +f32 = LW.fits_high(32n, 32n, n, f64)
176  %Equal.sym(WU.U64, X.mul32(a, b), SW.of_nat(n), GB.mul32_of(a, b)) : {U32.to_nat(X.hi(_)) == C.high(32n, n) : Nat}
177  LW.vo(C.high(32n, n), f32)