ch02.6.htm

介绍asci设计的一本书

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&#8211;3 =</P>
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NA</P>
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1011</P>
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1100</P>
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1101</P>
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zero =</P>
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0000</P>
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0000 or 1000</P>
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1111 or 0000</P>
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0000</P>
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max. positive =</P>
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1111 = 15</P>
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0111 = 7</P>
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0111 = 7</P>
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0111 = 7</P>
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max. negative =</P>
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0000= 0</P>
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1111 = &#8211;7</P>
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1000 = &#8211;7</P>
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1000 = &#8211;8</P>
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addition =</P>
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S =  A + B</P>
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= addend + augend</P>
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&nbsp;</P>
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SG(A) = sign of A</P>
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S = A + B</P>
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<A NAME="pgfId=162334">
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<B CLASS="Keyword">
if</B>
 SG(A) = SG(B) <B CLASS="Keyword">
then</B>
 S = A + B</P>
<P CLASS="TableLeft">
<A NAME="pgfId=162335">
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<B CLASS="Keyword">
else</B>
 {<B CLASS="Keyword">
if</B>
 B &lt; A <B CLASS="Keyword">
then</B>
 S = A &#8211; B</P>
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<A NAME="pgfId=162336">
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<B CLASS="Keyword">
else</B>
 S = B &#8211; A}</P>
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S = </P>
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A + B + COUT[MSB]</P>
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&nbsp;</P>
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COUT is carry out</P>
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S = A + B</P>
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addition result:</P>
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OV = overflow,</P>
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OR = out of range</P>
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OR = COUT[MSB]</P>
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&nbsp;</P>
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COUT is carry out</P>
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<B CLASS="Keyword">
if</B>
 SG(A) = SG(B) <B CLASS="Keyword">
then</B>
 OV = COUT[MSB]</P>
<P CLASS="TableLeft">
<A NAME="pgfId=191829">
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<B CLASS="Keyword">
else</B>
 OV = 0 (impossible)</P>
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OV =</P>
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 XOR(COUT[MSB], COUT[MSB&#8211;1])</P>
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OV = </P>
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XOR(COUT[MSB], COUT[MSB &#8211; 1])</P>
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SG(S) = sign of S </P>
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&nbsp;</P>
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S =  A + B</P>
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NA</P>
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<B CLASS="Keyword">
if</B>
 SG(A) = SG(B) <B CLASS="Keyword">
then</B>
 SG(S) = SG(A)</P>
<P CLASS="TableLeft">
<A NAME="pgfId=162369">
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<B CLASS="Keyword">
else</B>
 {<B CLASS="Keyword">
if</B>
 B &lt; A <B CLASS="Keyword">
then</B>
 SG(S) = SG(A)</P>
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<A NAME="pgfId=162370">
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<B CLASS="Keyword">
else</B>
 SG(S) = SG(B)}</P>
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NA</P>
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NA</P>
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subtraction =</P>
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D =  A &#8211; B</P>
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= minuend</P>
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 &#8211; subtrahend</P>
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D = A &#8211; B</P>
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SG(B) = NOT(SG(B));</P>
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D = A + B</P>
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Z = &#8211;B (negate);</P>
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D = A + Z</P>
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Z = &#8211;B (negate);</P>
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D = A + Z</P>
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subtraction result :</P>
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OV = overflow,</P>
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OR = out of range</P>
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OR = BOUT[MSB]</P>
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BOUT is borrow out</P>
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as in addition</P>
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as in addition</P>
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as in addition</P>
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negation :</P>
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Z = &#8211;A (negate)</P>
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