1 files changed, 103 insertions, 0 deletions
diff --git a/library/compiler-builtins/libm/src/math/atanf.rs b/library/compiler-builtins/libm/src/math/atanf.rs
new file mode 100644
index 00000000000..eb3d401cd96
--- /dev/null
+++ b/library/compiler-builtins/libm/src/math/atanf.rs
@@ -0,0 +1,103 @@
+/* origin: FreeBSD /usr/src/lib/msun/src/s_atanf.c */
+/*
+ * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
+ */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+use super::fabsf;
+
+const ATAN_HI: [f32; 4] = [
+    4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
+    7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
+    9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
+    1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
+];
+
+const ATAN_LO: [f32; 4] = [
+    5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
+    3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
+    3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
+    7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
+];
+
+const A_T: [f32; 5] =
+    [3.3333328366e-01, -1.9999158382e-01, 1.4253635705e-01, -1.0648017377e-01, 6.1687607318e-02];
+
+/// Arctangent (f32)
+///
+/// Computes the inverse tangent (arc tangent) of the input value.
+/// Returns a value in radians, in the range of -pi/2 to pi/2.
+#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
+pub fn atanf(mut x: f32) -> f32 {
+    let x1p_120 = f32::from_bits(0x03800000); // 0x1p-120 === 2 ^ (-120)
+
+    let z: f32;
+
+    let mut ix = x.to_bits();
+    let sign = (ix >> 31) != 0;
+    ix &= 0x7fffffff;
+
+    if ix >= 0x4c800000 {
+        /* if |x| >= 2**26 */
+        if x.is_nan() {
+            return x;
+        }
+        z = i!(ATAN_HI, 3) + x1p_120;
+        return if sign { -z } else { z };
+    }
+    let id = if ix < 0x3ee00000 {
+        /* |x| < 0.4375 */
+        if ix < 0x39800000 {
+            /* |x| < 2**-12 */
+            if ix < 0x00800000 {
+                /* raise underflow for subnormal x */
+                force_eval!(x * x);
+            }
+            return x;
+        }
+        -1
+    } else {
+        x = fabsf(x);
+        if ix < 0x3f980000 {
+            /* |x| < 1.1875 */
+            if ix < 0x3f300000 {
+                /*  7/16 <= |x| < 11/16 */
+                x = (2. * x - 1.) / (2. + x);
+                0
+            } else {
+                /* 11/16 <= |x| < 19/16 */
+                x = (x - 1.) / (x + 1.);
+                1
+            }
+        } else if ix < 0x401c0000 {
+            /* |x| < 2.4375 */
+            x = (x - 1.5) / (1. + 1.5 * x);
+            2
+        } else {
+            /* 2.4375 <= |x| < 2**26 */
+            x = -1. / x;
+            3
+        }
+    };
+    /* end of argument reduction */
+    z = x * x;
+    let w = z * z;
+    /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
+    let s1 = z * (i!(A_T, 0) + w * (i!(A_T, 2) + w * i!(A_T, 4)));
+    let s2 = w * (i!(A_T, 1) + w * i!(A_T, 3));
+    if id < 0 {
+        return x - x * (s1 + s2);
+    }
+    let id = id as usize;
+    let z = i!(ATAN_HI, id) - ((x * (s1 + s2) - i!(ATAN_LO, id)) - x);
+    if sign { -z } else { z }
+}