  We present fBLS -- a novel fast-folding technique to search for transiting
planets, based on the fast-folding algorithm (FFA), which is extensively used
in pulsar astronomy. For a given lightcurve with $N$ data points, fBLS
simultaneously produces all the binned phase-folded lightcurves for an array of
$N_p$ trial periods. For each folded lightcurve produced by fBLS, the algorithm
generates the standard BLS periodogram and statistics. The number of performed
arithmetic operations is $\mathcal{O}\big(N_p\cdot\log N_p \big)$, while
regular BLS requires $\mathcal{O}\big(N_p\cdot N\big)$ operations. fBLS can be
used to detect small rocky transiting planets, with periods shorter than one
day, a period range for which the computation is extensive. We demonstrate the
capabilities of the new algorithm by performing a preliminary fBLS search for
planets with ultra-short periods in the Kepler main-sequence lightcurves. In
addition, we developed a simplistic signal validation scheme for vetting the
planet candidates. This two-stage preliminary search identified all known
ultra-short planet candidates and found three new ones.
