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<div id="tabs-wrapper" class="clearfix"> <h1 class="with-tabs">Borland Real48 in Java</h1>
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<div id="node-191" class="node node-story node-promoted">
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<span class="submitted">24. January 2009 - 9:47 — <span class="username">Tilman</span></span>
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<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>When writing a converter tool for a binary file format, I had problems reading some of the floating point numbers. After a little bit of research I found out that this very special format was used in programs written in Borland Pascal/Delphi. Since I couldn't find any Java class that's able to read this kind of number I wrote it myself.</p>
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<p>As far as I remember these are basically reverse IEEE floating point numbers of six bytes. (It's been a while since I wrote this. See the PDF file by Richard Biffl for a detailed description of the format.)</p>
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<p>References:</p>
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<ul>
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<li><a href="http://www.wotsit.org/list.asp?search=Borland+Pascal+Real&button=GO!" title="Borland Pascal Real format information and C code">Borland Pascal Real format information and C code by Richard Biffl on wotsit.org</a></li>
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<li><a href="http://mail.python.org/pipermail/python-list/2001-December/117947.html" title="Algorithms for 6-byte ('real48') Borland Pascal Floating Point numbers">Real48 in Python by Martin Bless</a></li>
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</ul>
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<p>And here is the code:</p>
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<div class="geshifilter"><div class="java geshifilter-java"><span class="kw1">package</span> <span class="co2">de.tilman.util</span><span class="sy0">;</span><br />
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<br />
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<span class="kw1">import</span> <span class="co2">java.math.BigDecimal</span><span class="sy0">;</span><br />
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<br />
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<span class="co3">/**<br />
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* A class for representation and conversion of 6-byte/48-bit floating<br />
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* point numbers used in Borland Pascal/Delphi.<br />
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* <br />
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* @author Tilman Walther<br />
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*/</span><br />
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<span class="kw1">public</span> <span class="kw1">class</span> Real48 <span class="br0">{</span><br />
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<br />
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<span class="kw4">char</span><span class="br0">[</span><span class="br0">]</span> bytes<span class="sy0">;</span><br />
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<span class="kw4">double</span> value<span class="sy0">;</span><br />
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<br />
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<span class="co3">/**<br />
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* Represents a number in Real48 format.<br />
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* <br />
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* @param bytes the byte values of the number<br />
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*/</span><br />
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<span class="kw1">public</span> Real48<span class="br0">(</span><span class="kw4">char</span><span class="br0">[</span><span class="br0">]</span> bytes<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">this</span>.<span class="me1">bytes</span> <span class="sy0">=</span> bytes<span class="sy0">;</span><br />
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<span class="kw1">this</span>.<span class="me1">value</span> <span class="sy0">=</span> Real48.<span class="me1">getDoubleFromBytes</span><span class="br0">(</span>bytes<span class="br0">)</span><span class="sy0">;</span><br />
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<span class="br0">}</span><br />
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<br />
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<span class="co3">/**<br />
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* Returns the value of the number as double.<br />
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* <br />
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* @return the number as double<br />
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*/</span><br />
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<span class="kw1">public</span> <span class="kw4">double</span> getDoubleValue<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">return</span> value<span class="sy0">;</span><br />
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<span class="br0">}</span><br />
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<br />
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<span class="co3">/**<br />
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* Returns the byte values of the Real48 as char[].<br />
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* <br />
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* @return the byte values<br />
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*/</span><br />
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<span class="kw1">public</span> <span class="kw4">char</span><span class="br0">[</span><span class="br0">]</span> getBytes<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">return</span> bytes<span class="sy0">;</span><br />
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<span class="br0">}</span><br />
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<br />
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<span class="co3">/**<br />
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* Converts a Real48 in a double.<br />
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* <br />
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* @param bytes the number in Real48 format<br />
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* @return the number as double<br />
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*/</span><br />
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<span class="kw1">public</span> <span class="kw1">static</span> <span class="kw4">double</span> getDoubleFromBytes<span class="br0">(</span><span class="kw4">char</span><span class="br0">[</span><span class="br0">]</span> bytes<span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw4">long</span><span class="br0">[</span><span class="br0">]</span> real48 <span class="sy0">=</span> <span class="kw1">new</span> <span class="kw4">long</span><span class="br0">[</span><span class="nu0">6</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="sy0">;</span><br />
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real48<span class="br0">[</span><span class="nu0">5</span><span class="br0">]</span> <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">5</span><span class="br0">]</span><span class="sy0">;</span><br />
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<br />
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<span class="co1">// get sign</span><br />
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<span class="kw4">long</span> sign <span class="sy0">=</span> <span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy0">&</span> 0x80<span class="br0">)</span> <span class="sy0">>></span> <span class="nu0">7</span><span class="sy0">;</span><br />
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<br />
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<span class="co1">// get significand</span><br />
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<span class="kw4">long</span> significand <span class="sy0">=</span> <span class="br0">(</span><span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy0">%</span> 0x80<span class="br0">)</span> <span class="sy0"><<</span> <span class="nu0">32</span><span class="br0">)</span><br />
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<span class="sy0">+</span> <span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy0"><<</span> <span class="nu0">24</span><span class="br0">)</span><br />
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<span class="sy0">+</span> <span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span> <span class="sy0"><<</span> <span class="nu0">16</span><span class="br0">)</span><br />
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<span class="sy0">+</span> <span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span> <span class="sy0"><<</span> <span class="nu0">8</span><span class="br0">)</span><br />
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<span class="sy0">+</span> <span class="br0">(</span>real48<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span><span class="br0">)</span><span class="sy0">;</span><br />
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<br />
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<span class="co1">// get exponent</span><br />
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<span class="kw4">long</span> exponent <span class="sy0">=</span> bytes<span class="br0">[</span><span class="nu0">5</span><span class="br0">]</span><span class="sy0">;</span><br />
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<br />
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<span class="co1">// if the exponent is zero the real represents zero, too</span><br />
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<span class="kw1">if</span> <span class="br0">(</span>exponent <span class="sy0">==</span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span><br />
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<span class="kw1">return</span> <span class="nu0">0.0</span><span class="sy0">;</span><br />
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<span class="br0">}</span><br />
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<br />
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<span class="co1">// convert exponent (bias for Real48 is 129, bias for IEEE 754-double is 1023)</span><br />
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exponent <span class="sy0">+=</span> <span class="nu0">894</span><span class="sy0">;</span><br />
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<br />
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<span class="kw4">long</span> bits <span class="sy0">=</span> <span class="br0">(</span>sign <span class="sy0"><<</span> <span class="nu0">63</span><span class="br0">)</span> <span class="sy0">+</span> <span class="br0">(</span>exponent <span class="sy0"><<</span> <span class="nu0">52</span><span class="br0">)</span> <span class="sy0">+</span> <span class="br0">(</span>significand <span class="sy0"><<</span> <span class="nu0">13</span><span class="br0">)</span><span class="sy0">;</span><br />
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<br />
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<span class="kw4">double</span> value <span class="sy0">=</span> <a href="http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+double"><span class="kw3">Double</span></a>.<span class="me1">longBitsToDouble</span><span class="br0">(</span>bits<span class="br0">)</span><span class="sy0">;</span><br />
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<br />
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<span class="co1">// since Real48 has only a precision of 11 we need to set all digits > 11 to zero</span><br />
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<a href="http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+bigdecimal"><span class="kw3">BigDecimal</span></a> bd <span class="sy0">=</span> <span class="kw1">new</span> <a href="http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+bigdecimal"><span class="kw3">BigDecimal</span></a><span class="br0">(</span>value<span class="br0">)</span><span class="sy0">;</span><br />
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bd <span class="sy0">=</span> bd.<span class="me1">setScale</span><span class="br0">(</span><span class="nu0">11</span>, <a href="http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+bigdecimal"><span class="kw3">BigDecimal</span></a>.<span class="me1">ROUND_DOWN</span><span class="br0">)</span><span class="sy0">;</span><br />
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<br />
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<span class="kw1">return</span> bd.<span class="me1">doubleValue</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span><br />
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<span class="br0">}</span><br />
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<br />
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<span class="br0">}</span></div></div>
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<h2 class="title">Written by</h2>
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<ul class="menu"><li class="first leaf"><a href="../../blog/2/">Martin</a></li>
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<li class="last leaf"><a href="../../blog/3/">Tilman</a></li>
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