if haveFastIndex {
			if j := bytealg.Index(s[i-last:], b[:n]); j >= 0 {
				return i + j - last
			}
		} else {
			// If bytealg.Index is not available a brute force search is
			// ~1.5-3x faster than Rabin-Karp since n is small.
			c0 := b[last]
			c1 := b[last-1] // There are at least 2 chars to match
		loop:
			for ; i < len(s); i++ {
				if s[i] == c0 && s[i-1] == c1 {
					for k := 2; k < n; k++ {

	{"foofyfoobarfoobar", "y", 4},
	{"oooooooooooooooooooooo", "r", -1},
	{"oxoxoxoxoxoxoxoxoxoxoxoy", "oy", 22},
	{"oxoxoxoxoxoxoxoxoxoxoxox", "oy", -1},
	// test fallback to Rabin-Karp.
	{"000000000000000000000000000000000000000000000000000000000000000000000001", "0000000000000000000000000000000000000000000000000000000000000000001", 5},
	// test fallback to IndexRune
	{"oxoxoxoxoxoxoxoxoxoxox☺", "☺", 22},

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