From 1cb9f27c13481594469948ddbca982dd5ae4fad8 Mon Sep 17 00:00:00 2001 From: marcandre Date: Tue, 6 Nov 2012 17:11:06 +0000 Subject: * array.c (rb_ary_permutation): Support for Array#permutation.size [Feature #6636] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37501 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- array.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) (limited to 'array.c') diff --git a/array.c b/array.c index 2971b9c9a4..83c7e2c825 100644 --- a/array.c +++ b/array.c @@ -4323,6 +4323,29 @@ permute0(long n, long r, long *p, long index, char *used, VALUE values) } } +/* + * Returns the product of from, from-1, ..., from - how_many + 1. + * http://en.wikipedia.org/wiki/Pochhammer_symbol + */ +static VALUE +descending_factorial(long from, long how_many) +{ + VALUE cnt = LONG2FIX(how_many >= 0); + while(how_many-- > 0) { + cnt = rb_funcall(cnt, '*', 1, LONG2FIX(from--)); + } + return cnt; +} + +static VALUE +rb_ary_permutation_size(VALUE ary, VALUE args) +{ + long n = RARRAY_LEN(ary); + long k = (args && (RARRAY_LEN(args) > 0)) ? NUM2LONG(RARRAY_PTR(args)[0]) : n; + + return descending_factorial(n, k); +} + /* * call-seq: * ary.permutation { |p| block } -> ary @@ -4358,7 +4381,7 @@ rb_ary_permutation(int argc, VALUE *argv, VALUE ary) long r, n, i; n = RARRAY_LEN(ary); /* Array length */ - RETURN_ENUMERATOR(ary, argc, argv); /* Return Enumerator if no block */ + RETURN_SIZED_ENUMERATOR(ary, argc, argv, rb_ary_permutation_size); /* Return enumerator if no block */ rb_scan_args(argc, argv, "01", &num); r = NIL_P(num) ? n : NUM2LONG(num); /* Permutation size from argument */ -- cgit v1.2.3