nobu	2017-03-21 14:28:38 +0900 (Tue, 21 Mar 2017)

  New Revision: 58042

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=58042

  Log:
    string.c: use the usable size
    
    * string.c (rb_str_change_terminator_length): when called after
      the content has been copied, old terminator length no longer
      makes sense.  use the whole usable size instead of capacity
      without terminator.  [ruby-core:80257] [Bug #13339]

  Modified files:
    trunk/string.c
Index: string.c
===================================================================
--- string.c	(revision 58041)
+++ string.c	(revision 58042)
@@ -2102,11 +2102,11 @@ str_fill_term(VALUE str, char *s, long l https://github.com/ruby/ruby/blob/trunk/string.c#L2102
 void
 rb_str_change_terminator_length(VALUE str, const int oldtermlen, const int termlen)
 {
-    long capa = str_capacity(str, oldtermlen);
+    long capa = str_capacity(str, oldtermlen) + oldtermlen;
     long len = RSTRING_LEN(str);
 
     assert(capa >= len);
-    if (capa - len < termlen - oldtermlen) {
+    if (capa - len < termlen) {
 	rb_check_lockedtmp(str);
 	str_make_independent_expand(str, len, 0L, termlen);
     }
@@ -2118,7 +2118,7 @@ rb_str_change_terminator_length(VALUE st https://github.com/ruby/ruby/blob/trunk/string.c#L2118
 	if (!STR_EMBED_P(str)) {
 	    /* modify capa instead of realloc */
 	    assert(!FL_TEST((str), STR_SHARED));
-	    RSTRING(str)->as.heap.aux.capa = capa - (termlen - oldtermlen);
+	    RSTRING(str)->as.heap.aux.capa = capa - termlen;
 	}
 	if (termlen > oldtermlen) {
 	    TERM_FILL(RSTRING_PTR(str) + len, termlen);

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