From b8535a67f8a13d7b2f7727911649ad5e0396ff1a Mon Sep 17 00:00:00 2001
From: NAITOH Jun <naitoh@gmail.com>
Date: Fri, 18 Oct 2024 23:32:42 +0900
Subject: [PATCH] [JRuby] Optimize `scan()`: Remove duplicate `if (restLen() <
 pattern.size()) return context.nil;` checks in `!headonly`.

## Why?

https://github.com/ruby/strscan/blob/d31274f41b7c1e28f23d58cf7bfea03baa818cb7/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java#L371-L373

This means the following :

`if (str.size() - curr < pattern.size()) return context.nil;`

A similar check is made within `StringSupport#index()` within `!headonly`.

https://github.com/jruby/jruby/blob/be7815ec02356a58891c8727bb448f0c6a826d96/core/src/main/java/org/jruby/util/StringSupport.java#L1706-L1720

```Java
    public static int index(ByteList source, ByteList other, int offset, Encoding enc) {
        int sourceLen = source.realSize();
        int sourceBegin = source.begin();
        int otherLen = other.realSize();

        if (otherLen == 0) return offset;
        if (sourceLen - offset < otherLen) return -1;
```

- source = `strBL`
- other = `patternBL`
- offset = `strBeg + curr`

This means the following :
`if (strBL.realSize() - (strBeg + curr) < patternBL.realSize()) return -1;`

Both checks are the same.

## Benchmark

It shows String as a pattern is 2.40x faster than Regexp as a pattern.

```
$ benchmark-driver benchmark/check_until.yaml
Warming up --------------------------------------
              regexp     7.613M i/s -      7.593M times in 0.997350s (131.35ns/i)
          regexp_var     7.793M i/s -      7.772M times in 0.997364s (128.32ns/i)
              string    13.222M i/s -     13.199M times in 0.998297s (75.63ns/i)
          string_var    15.283M i/s -     15.216M times in 0.995667s (65.43ns/i)
Calculating -------------------------------------
              regexp    10.003M i/s -     22.840M times in 2.283361s (99.97ns/i)
          regexp_var     9.991M i/s -     23.378M times in 2.340019s (100.09ns/i)
              string    23.454M i/s -     39.666M times in 1.691221s (42.64ns/i)
          string_var    23.998M i/s -     45.848M times in 1.910447s (41.67ns/i)

Comparison:
          string_var:  23998466.3 i/s
              string:  23453777.5 i/s - 1.02x  slower
              regexp:  10002809.4 i/s - 2.40x  slower
          regexp_var:   9990580.1 i/s - 2.40x  slower
```
---
 .../org/jruby/ext/strscan/RubyStringScanner.java   | 14 ++++++--------
 test/strscan/test_stringscanner.rb                 |  6 ++++++
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
index a1e81effcd..7d3e7494fc 100644
--- a/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
+++ b/ext/jruby/org/jruby/ext/strscan/RubyStringScanner.java
@@ -265,7 +265,8 @@ private IRubyObject scan(ThreadContext context, IRubyObject regex, boolean succp
         check(context);
         clearMatched();
 
-        if (restLen() < 0) {
+        int restLen = restLen();
+        if (restLen < 0) {
             return context.nil;
         }
 
@@ -275,7 +276,7 @@ private IRubyObject scan(ThreadContext context, IRubyObject regex, boolean succp
         if (regex instanceof RubyRegexp) {
             pattern = ((RubyRegexp) regex).preparePattern(str);
 
-            int range = currPtr + restLen();
+            int range = currPtr + restLen;
 
             Matcher matcher = pattern.matcher(strBL.getUnsafeBytes(), matchTarget(), range);
             final int ret;
@@ -298,17 +299,14 @@ private IRubyObject scan(ThreadContext context, IRubyObject regex, boolean succp
             if (ret < 0) return context.nil;
         } else {
             RubyString pattern = regex.convertToString();
-
             Encoding patternEnc = str.checkEncoding(pattern);
-
-            if (restLen() < pattern.size()) {
-                return context.nil;
-            }
-
             ByteList patternBL = pattern.getByteList();
             int patternSize = patternBL.realSize();
 
             if (headonly) {
+                if (restLen < pattern.size()) {
+                    return context.nil;
+                }
                 if (ByteList.memcmp(strBL.unsafeBytes(), currPtr, patternBL.unsafeBytes(), patternBL.begin(), patternSize) != 0) {
                     return context.nil;
                 }
diff --git a/test/strscan/test_stringscanner.rb b/test/strscan/test_stringscanner.rb
index 9b7b7910d0..54fd5027cf 100644
--- a/test/strscan/test_stringscanner.rb
+++ b/test/strscan/test_stringscanner.rb
@@ -325,6 +325,9 @@ def test_scan_string
     s = create_string_scanner(str, false)
     matched = s.scan('str')
     assert_equal 'str', matched
+
+    s = create_string_scanner("str")
+    assert_equal nil, s.scan("str\0\0")
   end
 
   def test_skip
@@ -710,6 +713,9 @@ def test_scan_until_string
     assert_equal(nil, s.skip_until("Qux"))
     assert_equal("\u0000Baz", s.scan_until("Baz"))
     assert_equal(11, s.pos)
+
+    s = create_string_scanner("str")
+    assert_equal nil, s.scan_until("str\0\0")
   end
 
   def test_skip_until