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array.c: refine descending_factorial

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* array.c (descending_factorial): reduce factorial multipication.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59691 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
nobu 2017-08-30 07:55:19 +00:00
parent 6d5a4fefd0
commit 96223329d0
1 changed files with 10 additions and 4 deletions
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14
array.c
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@ -5079,10 +5079,16 @@ permute0(const long n, const long r, long *const p, char *const used, const VALU
static VALUE static VALUE
descending_factorial(long from, long how_many) descending_factorial(long from, long how_many)
{ {
VALUE cnt = LONG2FIX(how_many >= 0); VALUE cnt;
while (how_many-- > 0) { if (how_many > 0) {
VALUE v = LONG2FIX(from--); cnt = LONG2FIX(from);
cnt = rb_int_mul(cnt, v); while (--how_many > 0) {
long v = --from;
cnt = rb_int_mul(cnt, LONG2FIX(v));
}
}
else {
cnt = LONG2FIX(how_many == 0);
} }
return cnt; return cnt;
} }