This routine will take an 8 bit integer that corresponds to the numerator of a fraction whose denominator is 256 and find its arctangent. So the input ranges from 0 to 255 which corresponds to 0 to 255/256 = 0.996 . The output for an arctangent routine that returns a floating point number would be from 0 (atan(0)) to 0.783 (atan(255/256)) radians; or if you prefer, 0 to 44.89 degrees. However, this routine scales the output so that pi/4 radians (or 45 degrees) corresponds to 256. So for the input range of 0 to 255 you get an output of 0 to 255 ( atan(255/256) * 256 / (pi/4) is about 255). It's probably a little more interesting to see an intermediate data point or two:
P. Kilian, U. Ganse, und F. Spanier. Numerical Modeling of Space Plasma Flows (ASTRONUM2012), Volume 474 von Astronomical Society of the Pacific Conference Series, Seite 208. (April 2013)
V. Sundaresan, D. Maier, P. Ramarao, und M. Stoodley. Proceedings of the International Symposium on Code Generation and Optimization, Seite 87--97. Washington, DC, USA, IEEE Computer Society, (2006)
M. Ghanmare, M. Palpankar, M. Dutta, und M. Damle. International Journal on Recent and Innovation Trends in Computing and Communication, 3 (3):
1367--1370(März 2015)