http://idk.i2p/javadoc-i2p/net/i2p/crypto/eddsa/math/GroupElement.html
Preconditions: (TODO: Check this applies here)
$a[31] \le 127$ Parameters: a - $= a[0]+256*a[1]+\dots+256^{31} a[31]$ Returns: the GroupElement slide static byte[] slide (byte[] a) Calculates a sliding-windows base 2 representation for a given value $a$.
To learn more about it see [6] page 8. Output: $r$ which satisfies
$a = r0 * 2^0 + r1 * 2^1 + \dots + r255 * 2^{255}$ with $ri$ in $\{-15, -13, -11, -9, -7, -5, -3, -1, 0, 1, 3, 5, 7, 9, 11, 13, 15\}$ Method is package private only so...