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: f1600x.go
    path of file: ./repos/scan4all/vendor/github.com/cloudflare/circl/simd/keccakf1600
    
    the code of the file until where you have to start completion: // Package keccakf1600 provides a two and four-way Keccak-f[1600] permutation in parallel.
//
// Keccak-f[1600] is the permutation
    
func permuteScalarX2(a []uint64) {
	var buf [25]uint64
	for i := 0; i < 2; i++ {
		for j := 0; j < 25; j++ {
			buf[j] = a[2*j+i]
		}
		sha3.KeccakF1600(&buf)
		for j := 0; j < 25; j++ {
			a[2*j+i] = buf[j]
		}
	}
}