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| author | Damien George <damien.p.george@gmail.com> | 2017-06-23 15:52:00 +1000 |
|---|---|---|
| committer | Damien George <damien.p.george@gmail.com> | 2017-06-28 15:12:04 +1000 |
| commit | 045116551ec06d2619250cffff5e8b56a5f827d1 (patch) | |
| tree | 314e63ab9307cb0bc4d33486f173ced228209186 /lib/libm_dbl/atanh.c | |
| parent | 409fc8f9c1c5f07bcbdb6229196775deb4133e03 (diff) | |
| download | micropython-045116551ec06d2619250cffff5e8b56a5f827d1.tar.gz micropython-045116551ec06d2619250cffff5e8b56a5f827d1.zip | |
lib: Add libm_dbl, a double-precision math library, from musl-1.1.16.
Diffstat (limited to 'lib/libm_dbl/atanh.c')
| -rw-r--r-- | lib/libm_dbl/atanh.c | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/lib/libm_dbl/atanh.c b/lib/libm_dbl/atanh.c new file mode 100644 index 0000000000..63a035d706 --- /dev/null +++ b/lib/libm_dbl/atanh.c @@ -0,0 +1,29 @@ +#include "libm.h" + +/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */ +double atanh(double x) +{ + union {double f; uint64_t i;} u = {.f = x}; + unsigned e = u.i >> 52 & 0x7ff; + unsigned s = u.i >> 63; + double_t y; + + /* |x| */ + u.i &= (uint64_t)-1/2; + y = u.f; + + if (e < 0x3ff - 1) { + if (e < 0x3ff - 32) { + /* handle underflow */ + if (e == 0) + FORCE_EVAL((float)y); + } else { + /* |x| < 0.5, up to 1.7ulp error */ + y = 0.5*log1p(2*y + 2*y*y/(1-y)); + } + } else { + /* avoid overflow */ + y = 0.5*log1p(2*(y/(1-y))); + } + return s ? -y : y; +} |