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package mem
import (
"bytes"
)
// IndexPair returns the byte index of the first pair of two equal elements of
// size n.
//
// If no pairs of equal elements were found, -1 is returned.
func IndexPair(b []byte, n int) int {
if len(b)%n != 0 {
panic("input length is not a multiple of the item size")
}
// Delegate to indexPair to keep the function cost low and allow the size
// check to be inlined and the modulo optimized away for power of two sizes
// known at compile time.
return indexPair(b, n)
}
func indexPair(b []byte, n int) int {
switch n {
case 1:
return indexPair1(b)
case 2:
return indexPair2(b)
case 4:
return indexPair4(b)
case 8:
return indexPair8(b)
case 16:
return indexPair16(b)
case 32:
return indexPair32(b)
default:
return indexPairGeneric(b, n)
}
}
func indexPairGeneric(b []byte, n int) int {
for i := n; i < len(b); i += n {
if bytes.Equal(b[i-n:i], b[i:i+n]) {
return i - n
}
}
return -1
}
|
