Method Lookup2

ecgo/builder/api.go:311–339

Lookup2 performs a 2-bit lookup based on the given bits and values.

(b0, b1 frontend.Variable, i0, i1, i2, i3 frontend.Variable)

// Lookup2 performs a 2-bit lookup based on the given bits and values.
func (builder *builder) Lookup2(b0, b1 frontend.Variable, i0, i1, i2, i3 frontend.Variable) frontend.Variable {
	vars := []frontend.Variable{b0, b1, i0, i1, i2, i3}
	s0, s1 := vars[0], vars[1]
	in0, in1, in2, in3 := vars[2], vars[3], vars[4], vars[5]

	// ensure that bits are actually bits. Adds no constraints if the variables
	// are already constrained.
	builder.AssertIsBoolean(s0)
	builder.AssertIsBoolean(s1)

	// two-bit lookup for the general case can be done with three constraints as
	// following:
	//    (1) (in3 - in2 - in1 + in0) * s1 = tmp1 - in1 + in0
	//    (2) tmp1 * s0 = tmp2
	//    (3) (in2 - in0) * s1 = RES - tmp2 - in0
	// the variables tmp1 and tmp2 are new internal variables and the variables
	// RES will be the returned result

	tmp1 := builder.Add(in3, in0)
	tmp1 = builder.Sub(tmp1, in2, in1)
	tmp1 = builder.Mul(tmp1, s1)
	tmp1 = builder.Add(tmp1, in1)
	tmp1 = builder.Sub(tmp1, in0) // (1) tmp1 = s1 * (in3 - in2 - in1 + in0) + in1 - in0
	tmp2 := builder.Mul(tmp1, s0) // (2) tmp2 = tmp1 * s0
	res := builder.Sub(in2, in0)
	res = builder.Mul(res, s1)
	res = builder.Add(res, tmp2, in0) // (3) res = (v2 - v0) * s1 + tmp2 + in0
	return res
}

// IsZero returns 1 if the given variable is zero, otherwise returns 0.
func (builder *builder) IsZero(i1 frontend.Variable) frontend.Variable {