1 files changed, 89 insertions, 0 deletions
diff --git a/math/single/s_tanf.c b/math/single/s_tanf.c
new file mode 100644
index 0000000..f628165
--- /dev/null
+++ b/math/single/s_tanf.c
@@ -0,0 +1,89 @@
+/*
+ * s_tanf.c - single precision tangent function
+ *
+ * Copyright (c) 2009-2015, Arm Limited.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Source: my own head, and Remez-generated polynomial approximations.
+ */
+
+#include <math.h>
+#include "math_private.h"
+#include <errno.h>
+#include <fenv.h>
+#include "rredf.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+float ARM__tanf(float x)
+{
+    int q;
+
+    /*
+     * Range-reduce x to the range [-pi/4,pi/4].
+     */
+    {
+        /*
+         * I enclose the call to __mathlib_rredf in braces so that
+         * the address-taken-ness of qq does not propagate
+         * throughout the rest of the function, for what that might
+         * be worth.
+         */
+        int qq;
+        x = ARM__mathlib_rredf(x, &qq);
+        q = qq;
+    }
+    if (__builtin_expect(q < 0, 0)) { /* this signals tiny, inf, or NaN */
+        unsigned k = fai(x) << 1;
+        if (k < 0xFF000000)            /* tiny */
+            return FLOAT_CHECKDENORM(x);
+        else if (k == 0xFF000000)      /* inf */
+            return MATHERR_TANF_INF(x);
+        else                           /* NaN */
+            return FLOAT_INFNAN(x);
+    }
+
+    /*
+     * We use a direct polynomial approximation for tan(x) on
+     * [-pi/4,pi/4], and then take the negative reciprocal of the
+     * result if we're in an interval surrounding an odd rather than
+     * even multiple of pi/2.
+     *
+     * Coefficients generated by the command
+
+./auxiliary/remez.jl --variable=x2 --suffix=f -- '0' '(pi/BigFloat(4))^2' 5 0 'x==0 ? 1/BigFloat(3) : (tan(sqrt(x))-sqrt(x))/sqrt(x^3)' 'sqrt(x^3)'
+
+     */
+    {
+        float x2 = x*x;
+        x += x * (x2 * (
+                      3.333294809182307633621540045249152105330074691488121206914336806061620616979305e-01f+x2*(1.334274588580033216191949445078951865160600494428914956688702429547258497367525e-01f+x2*(5.315177279765676178198868818834880279286012428084733419724267810723468887753723e-02f+x2*(2.520300881849204519070372772571624013984546591252791443673871814078418474596388e-02f+x2*(2.051177187082974766686645514206648277055233230110624602600687812103764075834307e-03f+x2*(9.943421494628597182458186353995299429948224864648292162238582752158235742046109e-03f)))))
+                      ));
+        if (q & 1)
+            x = -1.0f/x;
+
+        return x;
+    }
+}
+
+#ifdef __cplusplus
+} /* end of extern "C" */
+#endif /* __cplusplus */
+
+/* end of s_tanf.c */