Source: sum_amd64.go in package golang.org/x/crypto/poly1305

go:build gc && !purego +build gc,!purego


package poly1305

go:noescape

func update(state *macState, msg []byte)

mac is a wrapper for macGeneric that redirects calls that would have gone to updateGeneric to update. Its Write and Sum methods are otherwise identical to the macGeneric ones, but using function pointers would carry a major performance cost.

type mac struct{ macGeneric }

func (h *mac) Write(p []byte) (int, error) {
	nn := len(p)
	if h.offset > 0 {
		n := copy(h.buffer[h.offset:], p)
		if h.offset+n < TagSize {
			h.offset += n
			return nn, nil
		}
		p = p[n:]
		h.offset = 0
		update(&h.macState, h.buffer[:])
	}
	if n := len(p) - (len(p) % TagSize); n > 0 {
		update(&h.macState, p[:n])
		p = p[n:]
	}
	if len(p) > 0 {
		h.offset += copy(h.buffer[h.offset:], p)
	}
	return nn, nil
}

func (h *mac) Sum(out *[16]byte) {
	state := h.macState
	if h.offset > 0 {
		update(&state, h.buffer[:h.offset])
	}
	finalize(out, &state.h, &state.s)