Function compileASCIIStringSetPrefixFilter

stringprefixfilter.go:225–263

compileASCIIStringSetPrefixFilter builds a byte-oriented multi-prefix scanner for the narrow shape where it beats running strings.Index once per prefix: case-sensitive ASCII prefixes with at least two prefixes sharing a first byte. It indexes possible first bytes with strings.IndexAny, then verifies

(prefixes []string, ignoreCase bool, minRequiredLength int)

// It indexes possible first bytes with strings.IndexAny, then verifies only the
// bucket for the byte found. Other shapes fall back to the old implementation.
func compileASCIIStringSetPrefixFilter(prefixes []string, ignoreCase bool, minRequiredLength int) (*asciiStringSetPrefixFilter, bool) {
	if ignoreCase {
		return nil, false
	}

	filter := &asciiStringSetPrefixFilter{
		minRequiredBytes: minRequiredLength,
	}
	var firstChars [256]bool
	var hasSharedFirst bool
	for _, prefix := range prefixes {
		if prefix == "" || !isASCIIString(prefix) {
			return nil, false
		}

		first := prefix[0]
		filter.prefixesByFirst[first] = append(filter.prefixesByFirst[first], prefix)
		if len(filter.prefixesByFirst[first]) > 1 {
			hasSharedFirst = true
		}
		firstChars[first] = true
	}

	if !hasSharedFirst {
		return nil, false
	}

	firstBytes := make([]byte, 0, len(prefixes)*2)
	for i, ok := range firstChars {
		if ok {
			firstBytes = append(firstBytes, byte(i))
		}
	}
	if len(firstBytes) == 0 {
		return nil, false
	}
	filter.firstChars = string(firstBytes)
	return filter, true
}

func (f *asciiStringSetPrefixFilter) index(input string, startAt int) (candidateByteIndex int, ok bool) {
	if !hasMinRequiredBytes(input, startAt, f.minRequiredBytes) {