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Altera_Forum's avatar
Altera_Forum
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17 years ago

signed/unsigned multipliers

I can't seem to find a way to instantiate a multiplier that will dynamically select between signed and unsigned multiplication. This is on a Cyclone II, but applies to other parts as well. Read...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
17 years ago

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Am I missing something?

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Yes. You need to sign extend 111 to 111111

so -1 x 3 = 


      11
+    11
+   11
+  11
+ 11
+11
--------
 111101 = -3

Sign extension just means take the MSB and keep adding it to the front to the input up to the length of the result. Unsigned numbers are really signed numbers with an implied '0' sign bit