src/compress/flate/copy.go

// Copyright 2012 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 flate

// forwardCopy is like the built-in copy function except that it always goes
// forward from the start, even if the dst and src overlap.
// It is equivalent to:
//   for i := 0; i < n; i++ {
//     mem[dst+i] = mem[src+i]
//   }
func forwardCopy(mem []byte, dst, src, n int) {
	if dst <= src {
		copy(mem[dst:dst+n], mem[src:src+n])
		return
	}
	for {
		if dst >= src+n {
			copy(mem[dst:dst+n], mem[src:src+n])
			return
		}
		// There is some forward overlap.  The destination
		// will be filled with a repeated pattern of mem[src:src+k].
		// We copy one instance of the pattern here, then repeat.
		// Each time around this loop k will double.
		k := dst - src
		copy(mem[dst:dst+k], mem[src:src+k])
		n -= k
		dst += k
	}
}