  In high dispersion spectra of rotating bodies such as stars and planets, the
rotation contributes significantly to, and sometimes dominates, the line
broadening. We present a simple method for rotationally broadening large
wavelength ranges of high-dispersion spectra. The broadening is rapid and
scales linearly with the length of the spectrum array. For large wavelength
ranges, the method is much faster than the popular convolution-based
broadening. We provide the code implementation of this method in a publicly
accessible repository.
