The accuracy is measured in absolute terms and slightly exceeds 9.6 decimal digits. Quadrant 0 is corresponds to angles of 0 to 90 degrees, quadrant 2 to 90 to 180 degrees, three to 180 to 270 degrees, and the fourth quadrant is the last 90 degrees of a circle. Different systems require a wide range of accuracy, from low precision fast approximations for real time imaging to slow but ultra-precise numbers for orbit corrections. Of course, where a coefficient is zero, remove that entire term from the polynomial to save two floating point operations. Integer Approximations Embedded systems are peculiar beasts.
Some applications demand very fast results with practically no accuracy.
Sometimes we have no floating point capability at all, and just need a rough integer result. The algorithms scale these numbers to integer approximations by multiplying by 255 or 65536. Theoretically this is a nice, fast way to compute a low precision integer sine. A crude alternative is to use a table lookup for the trig values. This might eat up a lot of memory, even if you only need a byte's worth of accuracy.