From 48f5f5915b0c357b05a9dda2732470bf67ebd691 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 diff --git a/array.c b/array.c index b99ab45..0fa3494 100644 --- a/array.c +++ b/array.c @@ -5796,14 +5796,17 @@ rb_ary_sum(int argc, VALUE *argv, VALUE ary) } if (RB_FLOAT_TYPE_P(e)) { - /* Kahan's compensated summation algorithm */ + /* + * Kahan-Babuska balancing compensated summation algorithm + * See http://link.springer.com/article/10.1007/s00607-005-0139-x + */ double f, c; f = NUM2DBL(v); c = 0.0; goto has_float_value; for (; i < RARRAY_LEN(ary); i++) { - double x, y, t; + double x, t; e = RARRAY_AREF(ary, i); if (block_given) e = rb_yield(e); @@ -5819,11 +5822,14 @@ rb_ary_sum(int argc, VALUE *argv, VALUE ary) else goto not_float; - 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; } + f += c; return DBL2NUM(f); not_float: diff --git a/enum.c b/enum.c index b328003..5a56dca 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) diff --git a/test/ruby/test_array.rb b/test/ruby/test_array.rb index 24a8eae..5ecaaa3 100644 --- a/test/ruby/test_array.rb +++ b/test/ruby/test_array.rb @@ -2821,6 +2821,7 @@ class TestArray < Test::Unit::TestCase assert_float_equal(large_number+(small_number*10), [large_number, *[small_number]*10].sum) assert_float_equal(large_number+(small_number*10), [large_number/1r, *[small_number]*10].sum) assert_float_equal(large_number+(small_number*11), [small_number, large_number/1r, *[small_number]*10].sum) + assert_float_equal(small_number, [large_number, small_number, -large_number].sum) assert_equal("abc", ["a", "b", "c"].sum("")) assert_equal([1, [2], 3], [[1], [[2]], [3]].sum([])) diff --git a/test/ruby/test_enum.rb b/test/ruby/test_enum.rb index 4ff4f88..c70ec7c 100644 --- a/test/ruby/test_enum.rb +++ b/test/ruby/test_enum.rb @@ -903,6 +903,7 @@ class TestEnumerable < Test::Unit::TestCase assert_float_equal(large_number+(small_number*10), [large_number, *[small_number]*10].each.sum) assert_float_equal(large_number+(small_number*10), [large_number/1r, *[small_number]*10].each.sum) assert_float_equal(large_number+(small_number*11), [small_number, large_number/1r, *[small_number]*10].each.sum) + assert_float_equal(small_number, [large_number, small_number, -large_number].each.sum) assert_equal("abc", ["a", "b", "c"].each.sum("")) assert_equal([1, [2], 3], [[1], [[2]], [3]].each.sum([])) -- cgit v0.10.2