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

     1  #include "libm.h"
     2  
     3  /* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
     4  float atanhf(float x)
     5  {
     6  	union {float f; uint32_t i;} u = {.f = x};
     7  	unsigned s = u.i >> 31;
     8  	float_t y;
     9  
    10  	/* |x| */
    11  	u.i &= 0x7fffffff;
    12  	y = u.f;
    13  
    14  	if (u.i < 0x3f800000 - (1<<23)) {
    15  		if (u.i < 0x3f800000 - (32<<23)) {
    16  			/* handle underflow */
    17  			if (u.i < (1<<23))
    18  				FORCE_EVAL((float)(y*y));
    19  		} else {
    20  			/* |x| < 0.5, up to 1.7ulp error */
    21  			y = 0.5f*log1pf(2*y + 2*y*y/(1-y));
    22  		}
    23  	} else {
    24  		/* avoid overflow */
    25  		y = 0.5f*log1pf(2*(y/(1-y)));
    26  	}
    27  	return s ? -y : y;
    28  }