[libre-riscv-dev] [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal

Mitchalsup mitchalsup at aol.com
Sun Sep 15 15:15:38 BST 2019

Mitch AlsupMitchAlsup at aol.com

-----Original Message-----
From: lkcl <luke.leighton at gmail.com>
To: RISC-V ISA Dev <isa-dev at groups.riscv.org>
Cc: programmerjake <programmerjake at gmail.com>; luke.leighton <luke.leighton at gmail.com>; allen.baum <allen.baum at esperantotech.com>; libre-riscv-dev <libre-riscv-dev at lists.libre-riscv.org>
Sent: Sat, Sep 14, 2019 5:25 pm
Subject: Re: [isa-dev] Re: FP transcendentals (trigonometry, root/exp/log) proposal

On Saturday, September 14, 2019 at 10:50:15 PM UTC+1, MitchAlsup wrote: 
When you get a multi-generational customer, which has an existing application;the first thing that customer will do is to run a sanity check of the new HW implementation using a "reference" benchmark. When any bit of the output of that program mismatches any bit from thenew implementation, the multi-generational customer will not be able to rationalize that this newHW is acceptable or not. This leads to various consternation,..... This happened to me at GOULD S.E.L circa 1982 when the new, faster, HW had more accurate FP implementation. 

rright.  ok.  so let me just check.  it's not the accuracy setting that you're objecting to / red-flag-raising, it's the "if less accurate is set you're allowed to be *more* accurate", is that correct?
i am reminded of a message by hendrik [allo similarly old person, told ya your input was valuable :) ] on iibre-riscv-dev a couple months back about how Ahmdahl got similar customer complaints, and had to have an OS patch providing *EXACTLY* bit-for-bit the brain-dead broken FP accuracy of the mainframe that Ahmdahl were copying.
is this what you're referring to, Mitch?
This is the basic problem; Yes.

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