You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: fe.go
    path of file: ./repos/cointop/vendor/golang.org/x/crypto/curve25519/internal/field
    
    the code of the file until where you have to start completion: // Copyright (c) 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package field implements fast arithmetic modulo 2^255-19.
package field

import (
	"crypto/subtle"
	"encoding/binary"
	"math/bits"
)

// Element represents an element of the field GF(2^255-19). Note that this
// is not a cryptographically secure group, and should only be used to interact
// with edwards25519.P
    
func (r *Element) SqrtRatio(u, v *Element) (rr *Element, wasSquare int) {
	var a, b Element

	// r = (u * v3) * (u * v7)^((p-5)/8)
	v2 := a.Square(v)
	uv3 := b.Multiply(u, b.Multiply(v2, v))
	uv7 := a.Multiply(uv3, a.Square(v2))
	r.Multiply(uv3, r.Pow22523(uv7))

	check := a.Multiply(v, a.Square(r)) // check = v * r^2

	uNeg := b.Negate(u)
	correctSignSqrt := check.Equal(u)
	flippedSignSqrt := check.Equal(uNeg)
	flippedSignSqrtI := check.Equal(uNeg.Multiply(uNeg, sqrtM1))

	rPrime := b.Multiply(r, sqrtM1) // r_prime = SQRT_M1 * r
	// r = CT_SELECT(r_prime IF flipped_sign_sqrt | flipped_sign_sqrt_i ELSE r)
	r.Select(rPrime, r, flippedSignSqrt|flippedSignSqrtI)

	r.Absolute(r) // Choose the nonnegative square root.
	return r, correctSignSqrt | flippedSignSqrt
}