CrossWorks for ARM User Guide

atanSynopsisDescriptionPortability#include double atan(double x);atan returns the principal value, in radians, of the inverse circular tangent of x. Theprincipal value lies in the interval [-¾?, +¾?] radians.atan conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).See Also atan2 (page 258)atan2SynopsisDescriptionFast math librarybehaviorIEC 60559 mathlibrary behaviorPortability#include double atan2(double y, double x);atan2 returns the value, in radians, of the inverse circular tangent of y divided by xusing the signs of x and y to compute the quadrant of the return value. The principalvalue lies in the interval [-PI/2, +PI/2] radians.If x = y = 0, errno (page 247) is set to EDOM and atan2 returns HUGE_VAL.atan2f(x, NaN) is NaNatan2f(NaN, x) is NaNatan2f(0, +(anything but NaN)) is 0atan2f(0, -(anything but NaN)) is ?atan2f((anything but 0 and NaN), 0) is ?/2atan2f((anything but Infinity and NaN), +Infinity) is 0atan2f((anything but Infinity and NaN), -Infinity) is ?atan2f(Infinity, +Infinity) is ?/4atan2f(Infinity, -Infinity) is 3?/4atan2f(Infinity, (anything but 0, NaN, and Infinity)) is ?/2atan2 conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).See Also atan (page 258)atan2fSynopsisDescription#include float atan2f(float y, float x);atan2f returns the value, in radians, of the inverse circular tangent of y divided by xusing the signs of x and y to compute the quadrant of the return value. The principalvalue lies in the interval [-PI/2, +PI/2] radians.258 Chapter 28 Standard C Library Reference