Index: fusl/src/math/atanhf.c |
diff --git a/fusl/src/math/atanhf.c b/fusl/src/math/atanhf.c |
new file mode 100644 |
index 0000000000000000000000000000000000000000..65f07c0f4f26e302f98ee4cc75b471c4204ee829 |
--- /dev/null |
+++ b/fusl/src/math/atanhf.c |
@@ -0,0 +1,28 @@ |
+#include "libm.h" |
+ |
+/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */ |
+float atanhf(float x) |
+{ |
+ union {float f; uint32_t i;} u = {.f = x}; |
+ unsigned s = u.i >> 31; |
+ float_t y; |
+ |
+ /* |x| */ |
+ u.i &= 0x7fffffff; |
+ y = u.f; |
+ |
+ if (u.i < 0x3f800000 - (1<<23)) { |
+ if (u.i < 0x3f800000 - (32<<23)) { |
+ /* handle underflow */ |
+ if (u.i < (1<<23)) |
+ FORCE_EVAL((float)(y*y)); |
+ } else { |
+ /* |x| < 0.5, up to 1.7ulp error */ |
+ y = 0.5f*log1pf(2*y + 2*y*y/(1-y)); |
+ } |
+ } else { |
+ /* avoid overflow */ |
+ y = 0.5f*log1pf(2*(y/(1-y))); |
+ } |
+ return s ? -y : y; |
+} |