  We present an algorithm for the numerical calculation of one-loop QCD
amplitudes. The algorithm consists of subtraction terms, approximating the
soft, collinear and ultraviolet divergences of one-loop amplitudes and a method
to deform the integration contour for the loop integration into the complex
space. The algorithm is formulated at the amplitude level and does not rely on
Feynman graphs. Therefore all required ingredients can be calculated
efficiently using recurrence relations. The algorithm applies to massless
partons as well as to massive partons.
