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package spray.json
/**
* Helper that creates strings that all share the same hashCode == 0.
*
* Adapted from MIT-licensed code by Andriy Plokhotnyuk
* at https://github.com/plokhotnyuk/jsoniter-scala/blob/26b5ecdd4f8c2ab7e97bd8106cefdda4c1e701ce/jsoniter-scala-benchmark/src/main/scala/com/github/plokhotnyuk/jsoniter_scala/macros/HashCodeCollider.scala#L6.
*/
object HashCodeCollider {
val visibleChars = (33 until 127).filterNot(c => c == '\\' || c == '"')
def asciiChars: Iterator[Int] = visibleChars.toIterator
def asciiCharsAndHash(previousHash: Int): Iterator[(Int, Int)] = visibleChars.toIterator.map(c => c -> (previousHash + c) * 31)
/** Creates an iterator of Strings that all have hashCode == 0 */
def zeroHashCodeIterator(): Iterator[String] =
for {
(i0, h0) <- asciiCharsAndHash(0)
(i1, h1) <- asciiCharsAndHash(h0)
(i2, h2) <- asciiCharsAndHash(h1) if (((h2 + 32) * 923521) ^ ((h2 + 127) * 923521)) < 0
(i3, h3) <- asciiCharsAndHash(h2) if (((h3 + 32) * 29791) ^ ((h3 + 127) * 29791)) < 0
(i4, h4) <- asciiCharsAndHash(h3) if (((h4 + 32) * 961) ^ ((h4 + 127) * 961)) < 0
(i5, h5) <- asciiCharsAndHash(h4) if (((h5 + 32) * 31) ^ ((h5 + 127) * 31)) < 0
(i6, h6) <- asciiCharsAndHash(h5) if ((h6 + 32) ^ (h6 + 127)) < 0
(i7, h7) <- asciiCharsAndHash(h6) if h6 + i7 == 0
} yield new String(Array(i0, i1, i2, i3, i4, i5, i6, i7).map(_.toChar))
}
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