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Hi,
this adds another missing method to StrictMath, mauve test is already in.
Comments or approval, appreciated.
Thanks,
Carsten
2006-08-02 Carsten Neumann <[EMAIL PROTECTED]>
* java/lang/StrictMath.java (tanh): New method.
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Index: cp/classpath/java/lang/StrictMath.java
===================================================================
--- cp.orig/classpath/java/lang/StrictMath.java 2006-08-02 19:17:29.000000000 +0200
+++ cp/classpath/java/lang/StrictMath.java 2006-08-02 19:21:06.000000000 +0200
@@ -814,6 +814,77 @@
}
/**
+ * Returns the hyperbolic tangent of <code>x</code>, which is defined as
+ * (exp(x) - exp(-x)) / (exp(x) + exp(-x)), i.e. sinh(x) / cosh(x).
+ *
+ Special cases:
+ * <ul>
+ * <li>If the argument is NaN, the result is NaN</li>
+ * <li>If the argument is positive infinity, the result is 1.</li>
+ * <li>If the argument is negative infinity, the result is -1.</li>
+ * <li>If the argument is zero, the result is zero.</li>
+ * </ul>
+ *
+ * @param x the argument to <em>tanh</em>
+ * @return the hyperbolic tagent of <code>x</code>
+ *
+ * @since 1.5
+ */
+ public static double tanh(double x)
+ {
+ // Method :
+ // 0. tanh(x) is defined to be (exp(x) - exp(-x)) / (exp(x) + exp(-x))
+ // 1. reduce x to non-negative by tanh(-x) = -tanh(x).
+ // 2. 0 <= x <= 2^-55 : tanh(x) := x * (1.0 + x)
+ // -t
+ // 2^-55 < x <= 1 : tanh(x) := -----; t = expm1(-2x)
+ // t + 2
+ // 2
+ // 1 <= x <= 22.0 : tanh(x) := 1 - ----- ; t=expm1(2x)
+ // t + 2
+ // 22.0 < x <= INF : tanh(x) := 1.
+
+ double t, z;
+
+ long bits;
+ long h_bits;
+ long l_bits;
+
+ // handle special cases
+ if (x != x)
+ return Double.NaN;
+ if (x == Double.POSITIVE_INFINITY)
+ return 1.0;
+ if (x == Double.NEGATIVE_INFINITY)
+ return -1.0;
+
+ bits = Double.doubleToLongBits(x);
+ h_bits = getHighDWord(bits) & 0x7fffffffL; // ingnore sign
+ l_bits = getLowDWord(bits);
+
+ if (h_bits < 0x40360000L) // |x| < 22
+ {
+ if (h_bits < 0x3c800000L) // |x| < 2^-55
+ return x * (1.0 + x);
+
+ if (h_bits >= 0x3ff00000L) // |x| >= 1
+ {
+ t = expm1(2.0 * abs(x));
+ z = 1.0 - 2.0 / (t + 2.0);
+ }
+ else // |x| < 1
+ {
+ t = expm1(-2.0 * abs(x));
+ z = -t / (t + 2.0);
+ }
+ }
+ else // |x| >= 22
+ z = 1.0;
+
+ return (x >= 0) ? z : -z;
+ }
+
+ /**
* Returns the lower two words of a long. This is intended to be
* used like this:
* <code>getLowDWord(Double.doubleToLongBits(x))</code>.
