1#include "libm.h"
 2
 3#if FLT_EVAL_METHOD==2
 4#undef sqrtf
 5#define sqrtf sqrtl
 6#elif FLT_EVAL_METHOD==1
 7#undef sqrtf
 8#define sqrtf sqrt
 9#endif
10
11/* acosh(x) = log(x + sqrt(x*x-1)) */
12float acoshf(float x)
13{
14	union {float f; uint32_t i;} u = {x};
15	uint32_t a = u.i & 0x7fffffff;
16
17	if (a < 0x3f800000+(1<<23))
18		/* |x| < 2, invalid if x < 1 */
19		/* up to 2ulp error in [1,1.125] */
20		return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1)));
21	if (u.i < 0x3f800000+(12<<23))
22		/* 2 <= x < 0x1p12 */
23		return logf(2*x - 1/(x+sqrtf(x*x-1)));
24	/* x >= 0x1p12 or x <= -2 or nan */
25	return logf(x) + 0.693147180559945309417232121458176568f;
26}