Path: ...!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Thomas Koenig Newsgroups: comp.arch Subject: Re: Computer architects leaving Intel... Date: Tue, 24 Sep 2024 05:23:08 -0000 (UTC) Organization: A noiseless patient Spider Lines: 30 Message-ID: References: <2024Sep10.101932@mips.complang.tuwien.ac.at> <2024Sep11.123824@mips.complang.tuwien.ac.at> <867cbhgozo.fsf@linuxsc.com> <20240912142948.00002757@yahoo.com> <20240915001153.000029bf@yahoo.com> <20240915154038.0000016e@yahoo.com> <32a15246310ea544570564a6ea100cab@www.novabbs.org> <50cd3ba7c0cbb587a55dd67ae46fc9ce@www.novabbs.org> <7cBGO.169512$_o_3.43954@fx17.iad> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Tue, 24 Sep 2024 07:23:08 +0200 (CEST) Injection-Info: dont-email.me; posting-host="e4fc060bfe99b656beb5422538e16372"; logging-data="3255539"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX190aMGy9lRm6XlOTgqTM+N0itRBLkCnqL8=" User-Agent: slrn/1.0.3 (Linux) Cancel-Lock: sha1:HdYJgL4or1D293Ah/wKiH8kJqcs= Bytes: 3252 BGB-Alt schrieb: > On 9/22/2024 3:43 PM, Paul A. Clayton wrote: >> On 9/19/24 11:07 AM, EricP wrote: >> [snip] >>> If the multiplier is pipelined with a latency of 5 and throughput of 1, >>> then MULL takes 5 cycles and MULL,MULH takes 6. >>> >>> But those two multiplies still are tossing away 50% of their work. >> >> I do not remember how multipliers are actually implemented — and >> am not motivated to refresh my memory at the moment — but I >> thought a multiply low would not need to generate the upper bits, >> so I do not understand where your "50% of their work" is coming >> from. >> >> The high result needs the low result carry-out but not the rest of >> the result. (An approximate multiply high for multiply by >> reciprocal might be useful, avoiding the low result work. There >> might also be ways that a multiplier could be configured to also >> provide bit mixing similar to middle result for generating a >> hash?) >> > > I guess it might be interesting if one made a bigger multiplier out of > 4-bit multipliers, in a way similar to a 4-bit shift-add. If you look through the old TTL handbooks by TI, you will find how people did multipliers in the bit-slice age. They had 4 bit * 4 bit->8 bit multipliers (74274) or Booth recoding with a 74261 and then summed up the partial products using the 74275.