summaryrefslogtreecommitdiff
path: root/missing/tgamma.c
diff options
context:
space:
mode:
authorakr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2008-02-07 01:43:43 +0000
committerakr <akr@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2008-02-07 01:43:43 +0000
commit14373fc4db7440d39db4fd39297f2ed44cc990f2 (patch)
tree966d984fadcafb2d9046a161b1e170d99904a592 /missing/tgamma.c
parentb88ecbcffc30fdf8b5743003563e10a347c05b03 (diff)
* 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
Diffstat (limited to 'missing/tgamma.c')
-rw-r--r--missing/tgamma.c49
1 files changed, 49 insertions, 0 deletions
diff --git a/missing/tgamma.c b/missing/tgamma.c
new file mode 100644
index 0000000..a30108e
--- /dev/null
+++ b/missing/tgamma.c
@@ -0,0 +1,49 @@
+/* tgamma.c - public domain implementation of error function tgamma(3m)
+
+reference - Haruhiko Okumura: C-gengo niyoru saishin algorithm jiten
+ (New Algorithm handbook in C language) (Gijyutsu hyouron
+ sha, Tokyo, 1991) [in Japanese]
+ http://oku.edu.mie-u.ac.jp/~okumura/algo/
+*/
+
+/***********************************************************
+ gamma.c -- Gamma function
+***********************************************************/
+#include <math.h>
+#define PI 3.14159265358979324 /* $\pi$ */
+#define LOG_2PI 1.83787706640934548 /* $\log 2\pi$ */
+#define N 8
+
+#define B0 1 /* Bernoulli numbers */
+#define B1 (-1.0 / 2.0)
+#define B2 ( 1.0 / 6.0)
+#define B4 (-1.0 / 30.0)
+#define B6 ( 1.0 / 42.0)
+#define B8 (-1.0 / 30.0)
+#define B10 ( 5.0 / 66.0)
+#define B12 (-691.0 / 2730.0)
+#define B14 ( 7.0 / 6.0)
+#define B16 (-3617.0 / 510.0)
+
+static double
+loggamma(double x) /* the natural logarithm of the Gamma function. */
+{
+ double v, w;
+
+ v = 1;
+ while (x < N) { v *= x; x++; }
+ w = 1 / (x * x);
+ return ((((((((B16 / (16 * 15)) * w + (B14 / (14 * 13))) * w
+ + (B12 / (12 * 11))) * w + (B10 / (10 * 9))) * w
+ + (B8 / ( 8 * 7))) * w + (B6 / ( 6 * 5))) * w
+ + (B4 / ( 4 * 3))) * w + (B2 / ( 2 * 1))) / x
+ + 0.5 * LOG_2PI - log(v) - x + (x - 0.5) * log(x);
+}
+
+double tgamma(double x) /* Gamma function */
+{
+ if (x < 0)
+ return PI / (sin(PI * x) * exp(loggamma(1 - x)));
+ return exp(loggamma(x));
+}
+