1 files changed, 33 insertions, 0 deletions
diff --git a/src/math/acoshl.c b/src/math/acoshl.c
new file mode 100644
index 0000000..943cec1
--- /dev/null
+++ b/src/math/acoshl.c
@@ -0,0 +1,33 @@
+#include "libm.h"
+
+#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+long double acoshl(long double x)
+{
+	return acosh(x);
+}
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
+/* acosh(x) = log(x + sqrt(x*x-1)) */
+long double acoshl(long double x)
+{
+	union ldshape u = {x};
+	int e = u.i.se;
+
+	if (e < 0x3fff + 1)
+		/* 0 <= x < 2, invalid if x < 1 */
+		return log1pl(x-1 + sqrtl((x-1)*(x-1)+2*(x-1)));
+	if (e < 0x3fff + 32)
+		/* 2 <= x < 0x1p32 */
+		return logl(2*x - 1/(x+sqrtl(x*x-1)));
+	if (e & 0x8000)
+		/* x < 0 or x = -0, invalid */
+		return (x - x) / (x - x);
+	/* 0x1p32 <= x or nan */
+	return logl(x) + 0.693147180559945309417232121458176568L;
+}
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
+// TODO: broken implementation to make things compile
+long double acoshl(long double x)
+{
+	return acosh(x);
+}
+#endif