util.c: round nearly middle value

* util.c (ruby_dtoa): [EXPERIMENTAL] adjust the case that the
  Float value is close to the exact but unrepresentable middle
  value of two values in the given precision, as r55604.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55621 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 4 insertions, 0 deletions

diff --git a/util.c b/util.c
index 8c428b57f0..0b0c935832 100644
--- a/util.c
+++ b/util.c
@@ -3452,8 +3452,12 @@ ruby_dtoa(double d_, int mode, int ndigits, int *decpt, int *sign, char **rve)
                     ilim = i;
                 *s++ = '0' + (int)L;
                 if (i == ilim) {
+                    double x;
                     if (dval(d) > 0.5 + dval(eps))
                         goto bump_up;
+                    else if (!isinf(x = d_ * tens[ilim-1] + 0.5) &&
+                             dval(d) > modf(x, &x))
+                        goto bump_up;
                     else if (dval(d) < 0.5 - dval(eps)) {
                         while (*--s == '0') ;
                         s++;