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- #include "libm.h"
- /* acosh(x) = log(x + sqrt(x*x-1)) */
- double acosh(double x)
- {
- union {double f; uint64_t i;} u = {.f = x};
- unsigned e = u.i >> 52 & 0x7ff;
- /* x < 1 domain error is handled in the called functions */
- if (e < 0x3ff + 1)
- /* |x| < 2, up to 2ulp error in [1,1.125] */
- return log1p(x-1 + sqrt((x-1)*(x-1)+2*(x-1)));
- if (e < 0x3ff + 26)
- /* |x| < 0x1p26 */
- return log(2*x - 1/(x+sqrt(x*x-1)));
- /* |x| >= 0x1p26 or nan */
- return log(x) + 0.693147180559945309417232121458176568;
- }
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