From 2278d157f00b07ee3790e7dc68232169a34d4af2 Mon Sep 17 00:00:00 2001 From: mrkn Date: Tue, 6 Dec 2016 13:40:31 +0000 Subject: array.c, enum.c: change sum algorithm * array.c (rb_ary_sum): change the algorithm to Kahan-Babuska balancing summation to be more precise. [Feature #12871] [ruby-core:77771] * enum.c (sum_iter, enum_sum): ditto. * test_array.rb, test_enum.rb: add an assertion for the above change. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57001 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- enum.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'enum.c') diff --git a/enum.c b/enum.c index b328003425..5a56dca5c1 100644 --- a/enum.c +++ b/enum.c @@ -3644,8 +3644,11 @@ sum_iter(VALUE i, struct enum_sum_memo *memo) } } else if (RB_FLOAT_TYPE_P(v)) { - /* Kahan's compensated summation algorithm */ - double x, y, t; + /* + * Kahan-Babuska balancing compensated summation algorithm + * See http://link.springer.com/article/10.1007/s00607-005-0139-x + */ + double x, t; float_value: if (RB_FLOAT_TYPE_P(i)) @@ -3662,9 +3665,11 @@ sum_iter(VALUE i, struct enum_sum_memo *memo) goto some_value; } - y = x - c; - t = f + y; - c = (t - f) - y; + t = f + x; + if (fabs(f) >= fabs(x)) + c += ((f - t) + x); + else + c += ((x - t) + f); f = t; } else { @@ -3788,7 +3793,7 @@ enum_sum(int argc, VALUE* argv, VALUE obj) rb_block_call(obj, id_each, 0, 0, enum_sum_i, (VALUE)&memo); if (memo.float_value) { - return DBL2NUM(memo.f); + return DBL2NUM(memo.f + memo.c); } else { if (memo.n != 0) -- cgit v1.2.3