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-rw-r--r--enum.c17
1 files changed, 11 insertions, 6 deletions
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)