From 885f5974cdf65b59415837ae97f5a14ef1350670 Mon Sep 17 00:00:00 2001
From: Kacper <kacper@mail.openlinux.dev>
Date: Tue, 9 Dec 2025 19:20:15 +0100
Subject: feat: add gzip and new headers

---
 lib/libm/tanh.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 lib/libm/tanh.c

(limited to 'lib/libm/tanh.c')

diff --git a/lib/libm/tanh.c b/lib/libm/tanh.c
new file mode 100644
index 00000000..b32bf0b6
--- /dev/null
+++ b/lib/libm/tanh.c
@@ -0,0 +1,49 @@
+#include "libm.h"
+
+/* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x))
+ *         = (exp(2*x) - 1)/(exp(2*x) - 1 + 2)
+ *         = (1 - exp(-2*x))/(exp(-2*x) - 1 + 2)
+ */
+double tanh(double x)
+{
+	union {
+		double f;
+		uint64_t i;
+	} u = { .f = x };
+	uint32_t w;
+	int sign;
+	double_t t;
+
+	/* x = |x| */
+	sign = u.i >> 63;
+	u.i &= (uint64_t)-1 / 2;
+	x = u.f;
+	w = u.i >> 32;
+
+	if (w > 0x3fe193ea) {
+		/* |x| > log(3)/2 ~= 0.5493 or nan */
+		if (w > 0x40340000) {
+			/* |x| > 20 or nan */
+			/* note: this branch avoids raising overflow */
+			t = 1 - 0 / x;
+		} else {
+			t = expm1(2 * x);
+			t = 1 - 2 / (t + 2);
+		}
+	} else if (w > 0x3fd058ae) {
+		/* |x| > log(5/3)/2 ~= 0.2554 */
+		t = expm1(2 * x);
+		t = t / (t + 2);
+	} else if (w >= 0x00100000) {
+		/* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */
+		t = expm1(-2 * x);
+		t = -t / (t + 2);
+	} else {
+		/* |x| is subnormal */
+		/* note: the branch above would not raise underflow in
+		 * [0x1p-1023,0x1p-1022) */
+		FORCE_EVAL((float)x);
+		t = x;
+	}
+	return sign ? -t : t;
+}
-- 
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