libc-top-half/musl/src/math/acoshf.c

   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)) */
  12 float 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 or nan */
  19                 /* up to 2ulp error in [1,1.125] */
  20                 return log1pf(x-1 + sqrtf((x-1)*(x-1)+2*(x-1)));
  21         if (a < 0x3f800000+(12<<23))
  22                 /* |x| < 0x1p12 */
  23                 return logf(2*x - 1/(x+sqrtf(x*x-1)));
  24         /* x >= 0x1p12 */
  25         return logf(x) + 0.693147180559945309417232121458176568f;
  26 }