// features seem to contribute similar slowdowns (~1.4x each).

	mask := maskOf(types)
	for i := 0; i < len(in.events); {
		ev := in.events[i]
		if ev.index > i {
			// push
			if ev.typ&mask != 0 {
				f(ev.node)
			}
			pop := ev.index
			if in.events[pop].typ&mask == 0 {
				// Subtrees do not contain types: skip them and pop.
				i = pop + 1
				continue
			}
		}

		return 1 << nUnaryExpr
	case *ast.ValueSpec:
		return 1 << nValueSpec
	}
	return 0
}

func maskOf(nodes []ast.Node) uint64 {
	if nodes == nil {
		return math.MaxUint64 // match all node types
	}
	var mask uint64
	for _, n := range nodes {
		mask |= typeOf(n)
	}
	return mask

	// Rewrite mask to apply after the final left shift.
	mask_3 := (mask_1 & mask_2) << uint(GetPPC64Shiftsh(sld))

	r_1 := 32 - srw
	r_2 := GetPPC64Shiftsh(sld)
	r_3 := (r_1 + r_2) & 31 // This can wrap.

	if uint64(uint32(mask_3)) != mask_3 || mask_3 == 0 {
		return 0
	}
	return encodePPC64RotateMask(int64(r_3), int64(mask_3), 32)
}

		return rune(p0&mask2)<<6 | rune(b1&maskx), 2
	}
	b2 := p[2]
	if b2 < locb || hicb < b2 {
		return RuneError, 1
	}
	if sz <= 3 {
		return rune(p0&mask3)<<12 | rune(b1&maskx)<<6 | rune(b2&maskx), 3
	}
	b3 := p[3]
	if b3 < locb || hicb < b3 {
		return RuneError, 1
	}
	return rune(p0&mask4)<<18 | rune(b1&maskx)<<12 | rune(b2&maskx)<<6 | rune(b3&maskx), 4
}

	}

	var mask image.Image
	switch mcm {
	case nil:
		// No-op.
	case color.AlphaModel:
		mask1 := image.NewAlpha(image.Rect(0, 0, srcw, srch))
		for y := 0; y < srch; y++ {
			for x := 0; x < srcw; x++ {
				a := uint8((23*x + 29*y) % 0x100)
				// Glyph masks are typically mostly zero,
				// so we only set a quarter of mask1's pixels.
				if a >= 0xc0 {

	src0 := image.NewRGBA(image.Rect(0, 0, 100, 100))
	mask0 := image.NewRGBA(image.Rect(0, 0, 100, 100))
	for _, c := range clipTests {
		dst := dst0.SubImage(c.dr).(*image.RGBA)
		src := src0.SubImage(c.sr).(*image.RGBA)
		r, sp, mp := c.r, c.sp, c.mp
		if c.nilMask {
			clip(dst, &r, src, &sp, nil, nil)
		} else {
			clip(dst, &r, src, &sp, mask0.SubImage(c.mr), &mp)
		}

// cidr('::1/128').ip().family() // returns '6'
// cidr('192.168.0.0/24').masked() // returns cidr('192.168.0.0/24')
// cidr('192.168.0.1/24').masked() // returns cidr('192.168.0.0/24')
// cidr('192.168.0.0/24') == cidr('192.168.0.0/24').masked() // returns true, CIDR was already in canonical format
// cidr('192.168.0.1/24') == cidr('192.168.0.1/24').masked() // returns false, CIDR was not in canonical format

	if prefix.Addr().Is6() {
		n = t.rootV6
	}
	bitPosition := 0
	// mask the address for sanity
	address := prefix.Masked().Addr()
	// we can't check longer than the request mask
	mask := prefix.Bits()
	// walk the network bits of the prefix
	for bitPosition < mask {
		// Look for a child checking the bit position after the mask
		n = n.child[getBitFromAddr(address, bitPosition+1)]
		if n == nil {

					return
				}
			} else if mask0, ok := mask.(*image.Alpha); ok {
				switch src0 := src.(type) {
				case *image.Uniform:
					drawGlyphOver(dst0, r, src0, mask0, mp)
					return
				case *image.RGBA:
					drawRGBAMaskOver(dst0, r, src0, sp, mask0, mp)
					return
				case *image.Gray:
					drawGrayMaskOver(dst0, r, src0, sp, mask0, mp)
					return

		if i >= 56 {
			// we might have to write the length here if all fit in one block
			d.x[i] |= mask1b & length[i-56]
		}
	}

	// compress, and only keep the digest if all fit in one block
	block(d, d.x[:])

	var digest [Size]byte
	for i, s := range d.h {
		digest[i*4] = mask1b & byte(s>>24)
		digest[i*4+1] = mask1b & byte(s>>16)
		digest[i*4+2] = mask1b & byte(s>>8)