math: tanh.c cleanup similar to sinh, cosh

[musl] / src / math / tanhf.c

diff --git a/src/math/tanhf.c b/src/math/tanhf.c
index 7cb459d..8099ec3 100644 (file)
--- a/src/math/tanhf.c
+++ b/src/math/tanhf.c
@@ -1,55 +1,35 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_tanhf.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.
- * ====================================================
- */
-
 #include "libm.h"
 
-static const float
-tiny = 1.0e-30,
-huge = 1.0e30;
-
 float tanhf(float x)
 {
-       float t,z;
-       int32_t jx,ix;
+       union {float f; uint32_t i;} u = {.f = x};
+       uint32_t w;
+       int sign;
+       float t;
 
-       GET_FLOAT_WORD(jx, x);
-       ix = jx & 0x7fffffff;
+       /* x = |x| */
+       sign = u.i >> 31;
+       u.i &= 0x7fffffff;
+       x = u.f;
+       w = u.i;
 
-       /* x is INF or NaN */
-       if(ix >= 0x7f800000) {
-               if (jx >= 0)
-                       return 1.0f/x + 1.0f;  /* tanh(+-inf)=+-1 */
-               else
-                       return 1.0f/x - 1.0f;  /* tanh(NaN) = NaN */
-       }
-
-       if (ix < 0x41100000) {  /* |x| < 9 */
-               if (ix < 0x39800000) {  /* |x| < 2**-12 */
-                       /* tanh(tiny) = tiny with inexact */
-                       if (huge+x > 1.0f)
-                               return x;
-               }
-               if (ix >= 0x3f800000) {  /* |x|>=1  */
-                       t = expm1f(2.0f*fabsf(x));
-                       z = 1.0f - 2.0f/(t+2.0f);
+       if (w > 0x3f0c9f54) {
+               /* |x| > log(3)/2 ~= 0.5493 or nan */
+               if (w > 0x41200000) {
+                       /* |x| > 10 */
+                       t = 1 + 0/(x + 0x1p-120f);
                } else {
-                       t = expm1f(-2.0f*fabsf(x));
-                       z = -t/(t+2.0f);
+                       t = expm1f(2*x);
+                       t = 1 - 2/(t+2);
                }
-       } else {  /* |x| >= 9, return +-1 */
-               z = 1.0f - tiny;  /* raise inexact */
+       } else if (w > 0x3e82c578) {
+               /* |x| > log(5/3)/2 ~= 0.2554 */
+               t = expm1f(2*x);
+               t = t/(t+2);
+       } else {
+               /* |x| is small */
+               t = expm1f(-2*x);
+               t = -t/(t+2);
        }
-       return jx >= 0 ? z : -z;
+       return sign ? -t : t;
 }