◄Summary►  ◄Timings►
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Partial Arctangent
 
Syntax:  FPATAN
 
Finds the partial tangent by calculating Z = ARCTAN(Y / X). X is taken
from ST and Y from ST(1). On the 8087 and 80287, Y and X must be in the
range 0 ≤ Y < X < ∞. On the 80387, there is no restriction on X and Y. X
is popped from the stack and Z replaces Y in ST.
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