  Stellar oscillations give seismic information on the internal properties of
stars. Red giants are targets of interest since they present mixed modes, which
behave as pressure modes in the convective envelope and as gravity modes in the
radiative core. Mixed modes thus directly probe red giant cores, and allow in
particular the study of their mean core rotation. The high-quality data
obtained by CoRoT and Kepler satellites represent an unprecedented perspective
to obtain thousands of measurements of red giant core rotation, in order to
improve our understanding of stellar physics in deep stellar interiors. We
developed an automated method to obtain such core rotation measurements and
validated it for stars on the red giant branch. In this work, we particularly
focus on the specific application of this method to red giants having a rapid
core rotation. They show complex spectra where it is tricky to disentangle
rotational splittings from mixed-mode period spacings. We demonstrate that the
method based on the identification of mode crossings is precise and efficient.
The determination of the mean core rotation directly derives from the precise
measurement of the asymptotic period spacing {\Delta}{\Pi}1 and of the
frequency at which the crossing of the rotational components is observed.
