Method Cmp

ecgo/builder/api.go:358–383

Cmp compares i1 and i2 and returns 1 if i1>i2, 0 if i1=i2, -1 if i1<i2.

(i1, i2 frontend.Variable)

// Cmp compares i1 and i2 and returns 1 if i1>i2, 0 if i1=i2, -1 if i1<i2.
func (builder *builder) Cmp(i1, i2 frontend.Variable) frontend.Variable {
	nbBits := builder.field.FieldBitLen()
	// in AssertIsLessOrEq we omitted comparison against modulus for the left
	// side as if `a+r<b` implies `a<b`, then here we compute the inequality
	// directly.
	bi1 := bits.ToBinary(builder, i1, bits.WithNbDigits(nbBits))
	bi2 := bits.ToBinary(builder, i2, bits.WithNbDigits(nbBits))

	res := newVariable(builder.toVariableId(0))

	for i := builder.field.FieldBitLen() - 1; i >= 0; i-- {

		iszeroi1 := builder.IsZero(bi1[i])
		iszeroi2 := builder.IsZero(bi2[i])

		i1i2 := builder.And(bi1[i], iszeroi2)
		i2i1 := builder.And(bi2[i], iszeroi1)

		n := builder.Select(i2i1, -1, 0)
		m := builder.Select(i1i2, 1, n)

		res = newVariable(builder.toVariableId(builder.Select(builder.IsZero(res), m, res)))

	}
	return res
}

// Println is not implemented and will panic if called.
func (builder *builder) Println(a ...frontend.Variable) {