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* math.c (math_gamma): use a table for positive small integers.

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git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@23351 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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akr 2009-05-06 07:51:20 +00:00
parent 821831a290
commit c36aeb5360
2 changed files with 49 additions and 11 deletions
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4
ChangeLog
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@ -1,3 +1,7 @@
Wed May 6 16:50:20 2009 Tanaka Akira <akr@fsij.org>
* math.c (math_gamma): use a table for positive small integers.
Wed May 6 09:27:04 2009 Nobuyoshi Nakada <nobu@ruby-lang.org>
* README.ja: code for THINK_C does not exist already. [Bug #1435]

56
math.c
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@ -596,30 +596,64 @@ math_erfc(VALUE obj, VALUE x)
* [9, 362880.0, 362880]
* [10, 3628800.0, 3628800]
* [11, 39916800.0, 39916800]
* [12, 479001599.999999, 479001600]
* [13, 6227020800.00001, 6227020800]
* [14, 87178291199.9998, 87178291200]
* [12, 479001600.0, 479001600]
* [13, 6227020800.0, 6227020800]
* [14, 87178291200.0, 87178291200]
* [15, 1307674368000.0, 1307674368000]
* [16, 20922789888000.0, 20922789888000]
* [17, 3.55687428096001e+14, 355687428096000]
* [18, 6.40237370572799e+15, 6402373705728000]
* [17, 355687428096000.0, 355687428096000]
* [18, 6.402373705728e+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]
* [21, 5.109094217170944e+19, 51090942171709440000]
* [22, 1.1240007277776077e+21, 1124000727777607680000]
* [23, 2.5852016738885062e+22, 25852016738884976640000]
* [24, 6.204484017332391e+23, 620448401733239439360000]
* [25, 1.5511210043330954e+25, 15511210043330985984000000]
*
*/
static VALUE
math_gamma(VALUE obj, VALUE x)
{
static double fact_table[] = {
/* fact(0) */ 1.0,
/* fact(1) */ 1.0,
/* fact(2) */ 2.0,
/* fact(3) */ 6.0,
/* fact(4) */ 24.0,
/* fact(5) */ 120.0,
/* fact(6) */ 720.0,
/* fact(7) */ 5040.0,
/* fact(8) */ 40320.0,
/* fact(9) */ 362880.0,
/* fact(10) */ 3628800.0,
/* fact(11) */ 39916800.0,
/* fact(12) */ 479001600.0,
/* fact(13) */ 6227020800.0,
/* fact(14) */ 87178291200.0,
/* fact(15) */ 1307674368000.0,
/* fact(16) */ 20922789888000.0,
/* fact(17) */ 355687428096000.0,
/* fact(18) */ 6402373705728000.0,
/* fact(19) */ 121645100408832000.0,
/* fact(20) */ 2432902008176640000.0,
/* fact(21) */ 51090942171709440000.0,
/* fact(22) */ 1124000727777607680000.0,
/* fact(23)=25852016738884976640000 needs 56bit mantissa which is
* impossible to represent exactly in IEEE 754 double. */
};
double d0, d;
double intpart, fracpart;
Need_Float(x);
errno = 0;
d0 = RFLOAT_VALUE(x);
fracpart = modf(d0, &intpart);
if (fracpart == 0.0 &&
0 < intpart &&
(size_t)intpart <= sizeof(fact_table)/sizeof(*fact_table)) {
return DBL2NUM(fact_table[(int)intpart - 1]);
}
errno = 0;
d = tgamma(d0);
domain_check(d0, d, "gamma");
return DBL2NUM(d);