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#include "libm.h" // for __expo2, FORCE_EVAL
#include <math.h> // for cosh, exp, expm1
#include <stdint.h> // for uint64_t, uint32_t
/* cosh(x) = (exp(x) + 1/exp(x))/2
* = 1 + 0.5*(exp(x)-1)*(exp(x)-1)/exp(x)
* = 1 + x*x/2 + o(x^4)
*/
double cosh(double x)
{
union {
double f;
uint64_t i;
} u = { .f = x };
uint32_t w;
double t;
/* |x| */
u.i &= (uint64_t)-1 / 2;
x = u.f;
w = u.i >> 32;
/* |x| < log(2) */
if (w < 0x3fe62e42) {
if (w < 0x3ff00000 - (26 << 20)) {
/* raise inexact if x!=0 */
FORCE_EVAL(x + 0x1p120f);
return 1;
}
t = expm1(x);
return 1 + t * t / (2 * (1 + t));
}
/* |x| < log(DBL_MAX) */
if (w < 0x40862e42) {
t = exp(x);
/* note: if x>log(0x1p26) then the 1/t is not needed */
return 0.5 * (t + 1 / t);
}
/* |x| > log(DBL_MAX) or nan */
/* note: the result is stored to handle overflow */
t = __expo2(x, 1.0);
return t;
}
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