From: Nobuyoshi Nakada <nobu@...>
Date: 2007-09-21T17:05:41+09:00
Subject: [ruby-dev:31809] Re: rb_str_substr is much slower than rb_str_subpat

なかだです。

At Fri, 21 Sep 2007 05:37:59 +0900,
Nobuyoshi Nakada wrote in [ruby-dev:31806]:
> 1.9では、長い文字列に対するString#[]が、Fixnumを使ったときのほう
> がRegexpを使ったときよりも、格段に遅くなっています。

"-"[1,1]がIndexErrorになってしまっていたので、少々修正。


Index: string.c
===================================================================
--- string.c	(revision 13481)
+++ string.c	(working copy)
@@ -737,25 +737,41 @@ rb_str_substr(VALUE str, long beg, long 
     rb_encoding *enc = rb_enc_get(str);
     VALUE str2;
-    int slen = str_strlen(str, enc);
+    char *p, *s = RSTRING_PTR(str), *e = s + RSTRING_LEN(str);
 
     if (len < 0) return Qnil;
-    if (beg > slen) return Qnil;
-    if (beg < 0) {
-	beg += slen;
-	if (beg < 0) return Qnil;
+    if (!RSTRING_LEN(str)) {
+	len = 0;
     }
-    if (beg + len > slen) {
-	len = slen - beg;
+    if (beg < 0) {
+	if (len > -beg) len = -beg;
+	if (-beg * rb_enc_mbmaxlen(enc) < RSTRING_LEN(str) / 8) {
+	    beg = -beg;
+	    while (len++ < beg && (e = rb_enc_prev_char(s, e, enc)) != 0);
+	    p = e;
+	    if (!p) return Qnil;
+	    while (beg-- > 0 && (p = rb_enc_prev_char(s, p, enc)) != 0);
+	    if (!p) return Qnil;
+	    len = e - p;
+	    goto sub;
+	}
+	else {
+	    beg += str_strlen(str, enc);
+	    if (beg < 0) return Qnil;
+	}
     }
-    if (len < 0) {
-	len = 0;
+    else if (beg > 0 && beg > str_strlen(str, enc)) {
+	return Qnil;
     }
     if (len == 0) {
-	str2 = rb_str_new5(str,0,0);
+	p = 0;
+    }
+    else if ((p = str_nth(s, e, beg, enc)) == e) {
+	len = 0;
     }
     else {
-	char *p = str_nth(RSTRING_PTR(str), RSTRING_END(str), beg, enc);
-	str2 = rb_str_new5(str, p, str_offset(p, RSTRING_END(str), len, enc));
+	len = str_offset(p, e, len, enc);
     }
+  sub:
+    str2 = rb_str_new5(str, p, len);
     rb_enc_copy(str2, str);
     OBJ_INFECT(str2, str);


-- 
--- 僕の前にBugはない。
--- 僕の後ろにBugはできる。
    中田 伸悦