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diff --git a/src/math/s_tan.c b/src/math/s_tan.c
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+/* @(#)s_tan.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * 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.
+ * ====================================================
+ */
+
+/* tan(x)
+ * Return tangent function of x.
+ *
+ * kernel function:
+ *      __kernel_tan            ... tangent function on [-pi/4,pi/4]
+ *      __ieee754_rem_pio2      ... argument reduction routine
+ *
+ * Method.
+ *      Let S,C and T denote the sin, cos and tan respectively on
+ *      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
+ *      in [-pi/4 , +pi/4], and let n = k mod 4.
+ *      We have
+ *
+ *          n        sin(x)      cos(x)        tan(x)
+ *     ----------------------------------------------------------
+ *          0          S           C             T
+ *          1          C          -S            -1/T
+ *          2         -S          -C             T
+ *          3         -C           S            -1/T
+ *     ----------------------------------------------------------
+ *
+ * Special cases:
+ *      Let trig be any of sin, cos, or tan.
+ *      trig(+-INF)  is NaN, with signals;
+ *      trig(NaN)    is that NaN;
+ *
+ * Accuracy:
+ *      TRIG(x) returns trig(x) nearly rounded
+ */
+
+#include <math.h>
+#include "math_private.h"
+
+double
+tan(double x)
+{
+        double y[2],z=0.0;
+        int32_t n, ix;
+
+    /* High word of x. */
+        GET_HIGH_WORD(ix,x);
+
+    /* |x| ~< pi/4 */
+        ix &= 0x7fffffff;
+        if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
+
+    /* tan(Inf or NaN) is NaN */
+        else if (ix>=0x7ff00000) return x-x;            /* NaN */
+
+    /* argument reduction needed */
+        else {
+            n = __ieee754_rem_pio2(x,y);
+            return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even
+                                                        -1 -- n odd */
+        }
+}