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package rulesfn
// Substring returns the substring of the input provided. If the start or stop
// indexes are not valid for the input nil will be returned. If errors occur
// they will be added to the provided [ErrorCollector].
func SubString(input string, start, stop int, reverse bool) *string {
if start < 0 || stop < 1 || start >= stop || len(input) < stop {
return nil
}
for _, r := range input {
if r > 127 {
return nil
}
}
if !reverse {
v := input[start:stop]
return &v
}
rStart := len(input) - stop
rStop := len(input) - start
return SubString(input, rStart, rStop, false)
}
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