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# define TGSOURCE "atan.c"
#include <errno.h>
#include <math.h>
#include "_tgmath.h"
/** arc tangent **/
TYPE TGFN(atan)(TYPE x)
{
int MAXLOOPS = 10;
TYPE arctan = 0.0;
TYPE power = 1.0;
int i;
switch (fpclassify(x)) {
case FP_ZERO: return x;
case FP_INFINITE: return signbit(x) ? - M_PI_2 : M_PI_2;
default: break;
}
if (0) {
errno = ERANGE; /* The result cannot be represented */
/* RETURN_FAILURE(CONSTANT(HUGE_VAL), A range error occurred); */
return TGHUGE;
}
/* TODO: correct input domain */
/* TODO: tweak number of loops */
/* arctan x = x - x^3/3 + x^5/5 - x^7/7 ... */
for (i = 1; i < MAXLOOPS; i++) {
power *= x;
if (i % 4 == 1) {
arctan += power / i;
} else if (i % 4 == 3) {
arctan -= power / i;
}
}
/* RETURN_SUCCESS(a value in the range `[-PI()/2, +PI()/2]'); */
return arctan;
}
/***
compute the principal value of the arc tangent of ARGUMENT(x).
***/
/*
IMPLEMENTATION(The value returned on a domain error, CONSTANT(HUGE_VAL))
LINK(m)
STDC(1)
*/
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