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<title>13.11 Operators used in the definitions</title>

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<h2>
  <a name="1218764"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">13.11 	 Operators used in the definitions</font>
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<h3>
  <a name="1218769"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">Modulo operators</font>
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  <a name="1218770"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Arithmetic on addresses is done using modulo arithmetic. This means that there is no checking for errors and, if the calculation overflows, the result `wraps around' the range of values representable in the word length of the processor. For example, adding 1 to the address at the top of the address map produces the address of the byte at the bottom of the address map. </font>
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<p>
  <a name="1223382"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">There are also a number of instructions for performing modulo arithmetic, such as <strong>sum</strong> and <strong>prod</strong>. These operators are represented by the symbols `<font face=symbol>+</font>' and `<font face=symbol>-</font>'.</font>
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<h3>
  <a name="1218771"> </a><font color="#003366"  face="Verdana, Arial, Helvetica, sans-serif">Error conditions</font>
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  <a name="1218772"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">Any errors that can occur in instructions which are defined in terms of the modulo operators are indicated explicitly in the instruction description. For example the <strong>div</strong> (divide) instruction indicates the cases that can cause overflow, independently of the actual division:</font>
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  <a name="1218773"> </a><font size=2  face="Verdana, Arial, Helvetica, sans-serif">if ( <span class=Signal>Areg</span> = 0) or (( <span class=Signal>Breg</span> = <em>MostNeg</em> ) and ( <span class=Signal>Areg</span> = -1)) <br>{<br>

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