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array.c, enum.c: change sum algorithm

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* 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
This commit is contained in:
mrkn 2016-12-06 13:40:31 +00:00
parent 0cb1a2b812
commit 48f5f5915b
4 changed files with 24 additions and 11 deletions
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16
array.c
View file

@ -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:

17
enum.c
View file

@ -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)

1
test/ruby/test_array.rb
View file

@ -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([]))

1
test/ruby/test_enum.rb
View file

@ -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([]))