stringio.c: share strings

* ext/stringio/stringio.c (enc_subseq): share the return value and
  the buffer as possible.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55210 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Mon May 30 14:54:58 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/stringio/stringio.c (enc_subseq): share the return value and
+	  the buffer as possible.
+
 Mon May 30 14:50:25 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (str_substr, rb_str_aref): refactor not to create

ext/stringio/stringio.c

@@ -95,6 +95,14 @@ get_strio(VALUE self)
     return ptr;
 }
 
+static VALUE
+enc_subseq(VALUE str, long pos, long len, rb_encoding *enc)
+{
+    str = rb_str_subseq(str, pos, len);
+    rb_enc_associate(str, enc);
+    return str;
+}
+
 static VALUE
 strio_substr(struct StringIO *ptr, long pos, long len)
 {
@@ -105,7 +113,7 @@ strio_substr(struct StringIO *ptr, long pos, long len)
     if (len > rlen) len = rlen;
     if (len < 0) len = 0;
     if (len == 0) return rb_str_new(0,0);
-    return rb_enc_str_new(RSTRING_PTR(str)+pos, len, enc);
+    return enc_subseq(str, pos, len, enc);
 }
 
 #define StringIO(obj) get_strio(obj)
@@ -690,16 +698,18 @@ strio_getc(VALUE self)
 {
     struct StringIO *ptr = readable(self);
     rb_encoding *enc = get_enc(ptr);
+    VALUE str = ptr->string;
+    long pos = ptr->pos;
     int len;
     char *p;
 
-    if (ptr->pos >= RSTRING_LEN(ptr->string)) {
+    if (pos >= RSTRING_LEN(str)) {
 	return Qnil;
     }
-    p = RSTRING_PTR(ptr->string)+ptr->pos;
-    len = rb_enc_mbclen(p, RSTRING_END(ptr->string), enc);
+    p = RSTRING_PTR(str)+pos;
+    len = rb_enc_mbclen(p, RSTRING_END(str), enc);
     ptr->pos += len;
-    return rb_enc_str_new(p, len, enc);
+    return enc_subseq(str, pos, len, enc);
 }
 
 /*