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: sha1block_amd64.go
    path of file: ./repos/gccrs/libgo/go/crypto/sha1
    
    the code of the file until where you have to start completion: // Copyright 2016 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.

// +build ignore

package sha1

import "internal/cpu"

//go:noescape
func blockAVX2(dig *digest, p []byte)

//go:noescape
fun
    
func block(dig *digest, p []byte) {
	if useAVX2 && len(p) >= 256 {
		// blockAVX2 calculates sha1 for 2 block per iteration
		// it also interleaves precalculation for next block.
		// So it may read up-to 192 bytes past end of p
		// We may add checks inside blockAVX2, but this will
		// just turn it into a copy of blockAMD64,
		// so call it directly, instead.
		safeLen := len(p) - 128
		if safeLen%128 != 0 {
			safeLen -= 64
		}
		blockAVX2(dig, p[:safeLen])
		blockAMD64(dig, p[safeLen:])
	} else {
		blockAMD64(dig, p)
	}
}