Division/sqrt algorithm

[sally-aha]

Which algorithm does hardfloat use for division and square root?

[aswaterman]

There are two. DivSqrtRecF64 uses a quadratically convergent iterative algorithm, using a pre-multiplication to get a 10-ish-bit initial approximation. DivSqrtRecFN_small uses a straightforward one-bit-at-a-time algorithm.

[sally-aha]

Then how can I choose which one to use? Which performs better?
And does DivSqrtRecFN_small use SRT? If so, which radix?
Thank you very much for your reply.

[aswaterman]

It's too dependent on your application for me to provide an answer. The first option has latency of 25-ish cycles and throughput of 1/3 operations per cycle, but the area cost is high and the clock rate might be limited. The second option has latency of S-ish cycles (where S is the width of the significand) and has throughput of 1/S operations per cycle, but the area cost is low and it can run at higher clock rate.

[aswaterman]

DivSqrtRecFN_small doesn't use SRT; it's just one bit at a time.

[JonnySmith0011]

Does DivSqrtRecF64 use algorithm of Goldschmidt or Newton-Raphson? @aswaterman
And did you consider using the mainstream SRT algorithm?

[liwt07]

Hi, I want to generate the Verilog of the division. Could you please tell me how to generate Verilog from hardfloat files? Thank you so much.

[aamartin0000]

The original Verilog code is still available here: http://www.jhauser.us/arithmetic/HardFloat.html

[sequencer]

FYI. I had a bare configurable SRT in sequencer/arithmetic. I'll find some time to PR hardfloat this year.