github.com/afumu/libc@v0.0.6/musl/src/math/tanhf.c (about)

     1  #include "libm.h"
     2  
     3  float tanhf(float x)
     4  {
     5  	union {float f; uint32_t i;} u = {.f = x};
     6  	uint32_t w;
     7  	int sign;
     8  	float t;
     9  
    10  	/* x = |x| */
    11  	sign = u.i >> 31;
    12  	u.i &= 0x7fffffff;
    13  	x = u.f;
    14  	w = u.i;
    15  
    16  	if (w > 0x3f0c9f54) {
    17  		/* |x| > log(3)/2 ~= 0.5493 or nan */
    18  		if (w > 0x41200000) {
    19  			/* |x| > 10 */
    20  			t = 1 + 0/x;
    21  		} else {
    22  			t = expm1f(2*x);
    23  			t = 1 - 2/(t+2);
    24  		}
    25  	} else if (w > 0x3e82c578) {
    26  		/* |x| > log(5/3)/2 ~= 0.2554 */
    27  		t = expm1f(2*x);
    28  		t = t/(t+2);
    29  	} else if (w >= 0x00800000) {
    30  		/* |x| >= 0x1p-126 */
    31  		t = expm1f(-2*x);
    32  		t = -t/(t+2);
    33  	} else {
    34  		/* |x| is subnormal */
    35  		FORCE_EVAL(x*x);
    36  		t = x;
    37  	}
    38  	return sign ? -t : t;
    39  }