constraint optimizations for assertLeadingZeros

fri/fri.go

@@ -75,14 +75,8 @@ func (f *Chip) ToOpenings(c variables.OpeningSet) Openings {
 func (f *Chip) assertLeadingZeros(powWitness gl.Variable, friConfig types.FriConfig) {
 	// Asserts that powWitness'es big-endian bit representation has at least friConfig.ProofOfWorkBits leading zeros.
 	// Note that this is assuming that the Goldilocks field is being used.  Specfically that the
-	// field is 64 bits long
-	maxPowWitness := uint64(math.Pow(2, float64(64-friConfig.ProofOfWorkBits))) - 1
-
-	// TODO:  This does an un-nessary reduce, since powWitness is already range checked to be within GL field.
-	reducedPowWitness := f.gl.Reduce(powWitness)
-
-	// TODO:  Can replace with with std.rangecheck.Check.  Will probably be less contraints.
-	f.api.AssertIsLessOrEqual(reducedPowWitness.Limb, frontend.Variable(maxPowWitness))
+	// field is 64 bits long.
+	f.gl.RangeCheckWithMaxBits(powWitness, 64-friConfig.ProofOfWorkBits)
 }
 
 func (f *Chip) fromOpeningsAndAlpha(

goldilocks/base.go

@@ -333,6 +333,11 @@ func (p *Chip) RangeCheck(x Variable) {
 	)
 }
 
+// This function will assert that the field element x is less than 2^maxNbBits.
+func (p *Chip) RangeCheckWithMaxBits(x Variable, maxNbBits uint64) {
+	p.rangeChecker.Check(x.Limb, int(maxNbBits))
+}
+
 func (p *Chip) AssertIsEqual(x, y Variable) {
 	p.api.AssertIsEqual(x.Limb, y.Limb)
 }