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POEfficient strtod in Java?
 

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    <p>So I have this Java program that I use to munch through several terabytes of data. Performance is a concern.</p> <p>I've profiled the app, and a large fraction of all memory allocations as well as a large fraction of CPU time come from performing one simple operation:</p> <p>I have an array of ASCII chars. I know that the characters from offset <code>i</code> to offset <code>j</code> represent a floating-point number. I need to extract that floating-point number into a <code>double</code>.</p> <p>The naive <code>Double.parseDouble(new String(buf, i, j - i))</code> does the job. However, this is where a lot of time is spent and a lot of memory allocations come from, probably because:</p> <ul> <li><code>new String()</code> creates a new object, creates an internal <code>char[]</code> array and copies the characters into the array;</li> <li><code>Double.parseDouble()</code> creates a <a href="http://www.docjar.com/html/api/sun/misc/FloatingDecimal.java.html" rel="nofollow"><code>FloatingDecimal</code></a> object, and too creates a <code>char[]</code> array, also copying the characters into it.</li> </ul> <p>All these allocations and all this copying are not really necessary. Can I avoid them?</p> <p>What I'd really like is a <a href="http://en.wikipedia.org/wiki/Strtod" rel="nofollow"><code>strtod</code></a>-like function that would take a <code>char[]</code> (or a <code>byte[]</code>) as well as start/end offsets, and return a <code>double</code>.</p> <p>Any suggestions? Should I roll out my own? Should I write a JNI wrapper around <code>strtod</code>? Should I use some Java library that's already out there?</p>
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    1. COActually, String.substring method doesn't copy the initial array. It might be useful if String constructor is a bottleneck.
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