<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On Nov 6, 2013, at 11:30 AM, Peter Levart <<a href="mailto:peter.levart@gmail.com">peter.levart@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); display: inline !important; float: none; ">Well, indexOf(char) or lastIndexOf(char) searches for a single char. We can do better searching backwards for two chars at the same time.</span><br style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><br style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><span style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255); display: inline !important; float: none; ">If the "name" of VM-anonymous class is always ending with pattern: "slash followed by some decimal digits" then the following would be even faster:</span></blockquote></div><br><div>Although this reasoning is plausible, it is not a reliable conclusion, and should not drive edits of Java code without careful measurement. The reasoning assumes a performance model based on the interpreter and bytecode count. But performance depends on native code produced by the JIT.</div><div><br></div><div>An optimizing JIT will usually transform the code deeply. For string scanning, for example, HotSpot has an intrinsic for String.indexOf(String) that uses totally different code from a user-coded loop. (It is not currently so for String.indexOf(int), but String.indexOf("/") is potentially very fast.)</div><div><br></div><div>Also, with your example code, the combined loop may often be faster than two back-to-back loops, but simpler loops can sometimes be vectorized more robustly, to the point where back-to-back simple loops, if vectorized, may be competitive with a hand-fused loop.</div><div><br></div><div>So loop complexity and method intrinsics can create surprises for those who rely on simple performance modesl</div><div><br></div><div>Some day we will get to a world where loops are specified stream-wise, and robustly optimized without this sort of manual intervention. In the mean time, be careful about advising hand-optimizations of Java code. They can backfire, by confusing the JIT and preventing optimizations that would apply to simpler code.</div><div><br></div><div>— John</div></body></html>