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Authored by: jesse on Tuesday, October 16 2012 @ 11:02 AM EDT |
Besides using the half-adder, full adders are only used for about 4 bits. Last I
checked, there are layered formulas used "look ahead carry", that can
take the inputs to the 4 bit adders, and compute a carry for the next stage
while the 4bit adder is computing internally.
This does nothing but allow 4 bit adders to be operated parallel for as much as
desired.
Look-ahead-carry computations allow 64 bit values to be added in the time it
takes to operate a 4 bit adder.
Multiplies/divides can be done in one of two ways - table lookup (much faster
for most things) or using the old "shift and add"(multiply) or
"subtract-and-shift" (divide).
This was the source of the problem with the old Pentium multiplication errors -
one of the lookup tables was incomplete...[ Reply to This | Parent | # ]
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