From 14373fc4db7440d39db4fd39297f2ed44cc990f2 Mon Sep 17 00:00:00 2001
From: akr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Thu, 7 Feb 2008 01:43:43 +0000
Subject: * math.c (math_gamma): new method Math.gamma.   (math_lgamma): new
 method Math.lgamma.

* include/ruby/missing.h (tgamma): declared unless HAVE_TGAMMA.
  (lgamma_r): declared unless HAVE_LGAMMA_R.

* configure.in (tgamma): check for replacement funtions.
  (lgamma_r): ditto.

* missing/tgamma.c: new file.  based on gamma.c from
  "C-gengo niyoru saishin algorithm jiten" (New Algorithm handbook
  in C language) (Gijyutsu hyouron sha, Tokyo, 1991)
  by Haruhiko Okumura.

* missing/lgamma_r.c: ditto.

* LEGAL (missing/tgamma.c): describe as public domain.
  (missing/lgamma_r.c): ditto.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15388 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 math.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

(limited to 'math.c')

diff --git a/math.c b/math.c
index 332d89916d..3a4ed735a9 100644
--- a/math.c
+++ b/math.c
@@ -486,6 +486,76 @@ math_erfc(VALUE obj, VALUE x)
     return DOUBLE2NUM(erfc(RFLOAT_VALUE(x)));
 }
 
+/*
+ * call-seq:
+ *    Math.gamma(x)  => float
+ *
+ *  Calculates the gamma function of x.
+ *
+ *  Note that gamma(n) is same as fact(n-1) for integer n >= 0.
+ *  However gamma(n) returns float and possibly has error in calculation.
+ *
+ *   def fact(n) (1..n).inject(1) {|r,i| r*i } end
+ *   0.upto(25) {|i| p [i, Math.gamma(i+1), fact(i)] }
+ *   =>
+ *   [0, 1.0, 1]
+ *   [1, 1.0, 1]
+ *   [2, 2.0, 2]
+ *   [3, 6.0, 6]
+ *   [4, 24.0, 24]
+ *   [5, 120.0, 120]
+ *   [6, 720.0, 720]
+ *   [7, 5040.0, 5040]
+ *   [8, 40320.0, 40320]
+ *   [9, 362880.0, 362880]
+ *   [10, 3628800.0, 3628800]
+ *   [11, 39916800.0, 39916800]
+ *   [12, 479001599.999999, 479001600]
+ *   [13, 6227020800.00001, 6227020800]
+ *   [14, 87178291199.9998, 87178291200]
+ *   [15, 1307674368000.0, 1307674368000]
+ *   [16, 20922789888000.0, 20922789888000]
+ *   [17, 3.55687428096001e+14, 355687428096000]
+ *   [18, 6.40237370572799e+15, 6402373705728000]
+ *   [19, 1.21645100408832e+17, 121645100408832000]
+ *   [20, 2.43290200817664e+18, 2432902008176640000]
+ *   [21, 5.10909421717094e+19, 51090942171709440000]
+ *   [22, 1.12400072777761e+21, 1124000727777607680000]
+ *   [23, 2.58520167388851e+22, 25852016738884976640000]
+ *   [24, 6.20448401733239e+23, 620448401733239439360000]
+ *   [25, 1.5511210043331e+25, 15511210043330985984000000]
+ *
+ */
+
+static VALUE
+math_gamma(VALUE obj, VALUE x)
+{
+    Need_Float(x);
+    return DOUBLE2NUM(tgamma(RFLOAT_VALUE(x)));
+}
+
+/*
+ * call-seq:
+ *    Math.lgamma(x)  => [float, -1 or 1]
+ *
+ *  Calculates the logarithmic gamma of x and
+ *  the sign of gamma of x.
+ *
+ *  Math.lgamma(x) is same as
+ *   [Math.log(Math.gamma(x)), Math.gamma(x) < 0 ? -1 : 1]
+ *  but avoid overflow by Math.gamma(x) for large x.
+ */
+
+static VALUE
+math_lgamma(VALUE obj, VALUE x)
+{
+    int sign;
+    VALUE v;
+    Need_Float(x);
+    v = DOUBLE2NUM(lgamma_r(RFLOAT_VALUE(x), &sign));
+    return rb_assoc_new(v, INT2FIX(sign));
+}
+
 /*
  *  The <code>Math</code> module contains module functions for basic
  *  trigonometric and transcendental functions. See class
@@ -541,4 +611,7 @@ Init_Math(void)
 
     rb_define_module_function(rb_mMath, "erf",  math_erf,  1);
     rb_define_module_function(rb_mMath, "erfc", math_erfc, 1);
+
+    rb_define_module_function(rb_mMath, "gamma", math_gamma, 1);
+    rb_define_module_function(rb_mMath, "lgamma", math_lgamma, 1);
 }
-- 
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