alt Hacker NewsWhy do we make computers multiply single digit numbers, instead of taking the result from a lookup table, like humans do? To answer my own question, I am assuming it would be because multiplying would still be faster than reading from a lookup table? Any ideas?
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Every combinational logic function can be implemented as a look up table, which can be implemented as a hardware ROM. It is common to consider speed-power-area tradeoffs to find good implementations.
> I am assuming it would be because multiplying would still be faster than reading from a lookup table?
Even if it isn’t, it still would be a lot cheaper. With 32-bit integers, the lookup table would have 2⁶⁴ 64-bit values. If my math six right, that is 128 exabytes of read-only memory. With 64-but integers, it truly would be impractical, at 2¹²⁸ 128-bit values.
In a sense, they do exactly that! But since there are only two single-digit numbers in binary, it makes for a pretty short table.