Bug 43

Summary: create an IEEE754 FP "sqrt"
Product: Libre-SOC's first SoC Reporter: Luke Kenneth Casson Leighton <lkcl>
Component: ALU (including IEEE754 16/32/64-bit FPU)Assignee: Aleksandar Kostovic <alexandar.kostovic>
Status: PAYMENTPENDING FIXED    
Severity: enhancement CC: libre-soc-bugs
Priority: ---    
Version: unspecified   
Hardware: PC   
OS: Linux   
NLnet milestone: NLnet.2019.02.012 total budget (EUR) for completion of task and all subtasks: 1200
budget (EUR) for this task, excluding subtasks' budget: 1200 parent task for budget allocation: 48
child tasks for budget allocation: The table of payments (in EUR) for this task; TOML format:
# guessed date for lkcl lkcl={amount=480,paid=2019-08-10} programmerjake={amount=720,paid=2019-08-16}
Bug Depends on:    
Bug Blocks: 48    

Description Luke Kenneth Casson Leighton 2019-03-09 05:42:01 GMT 
this to be done using an adaptation (to Base 4) of the binary method:
https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)

adaptation to base 4 is 2-bits at a time.  this requires only 3 extra comparators and one extra adder (the adder being used to calculate a multiply by 3).  multiply by 0 is clearly 0.  multiply by 1 is clearly the original. multiply by 2 is a fixed-width shift.  multiply by 3 is an add (of number shifted added to original number).
Comment 2 Luke Kenneth Casson Leighton 2019-04-05 06:40:12 BST 
*** Bug 56 has been marked as a duplicate of this bug. ***
Comment 3 Aleksandar Kostovic 2019-04-25 04:57:13 BST 
Plan for thr further FPU development:

- create sqrt function
- create test for sqrt function
- run the tests for the whole FPU
Comment 4 Luke Kenneth Casson Leighton 2019-04-25 11:20:14 BST 
what i recommend instead is to create a milestone "preliminary
exploratory software emulation of FP SQRT" milestone.

context:
http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-April/001221.html
Comment 5 Luke Kenneth Casson Leighton 2019-04-25 11:26:17 BST 
(In reply to Aleksandar Kostovic from comment #3)
> Plan for thr further FPU development:
> 
> - create sqrt function
> - create test for sqrt function
> - run the tests for the whole FPU

so if you approve the idea "create preliminary software-only exploratory version"
can you please create a new bugreport, and set its "Blocks" field to 43 (this bug)?

also remember to "take ownership" of the bug, and to set the NLnet milestone field.

i need you to do more of this because i'm getting RSI and it's now very painful to type.
Comment 6 Luke Kenneth Casson Leighton 2019-04-25 20:25:19 BST 
> > paper) into python, which we will *need anyway as part of the unit
> > tests*.
> >

> Yes i will convert that code to python.

great.  look fwd to seeing it.  always wanted to impl.
Comment 7 Luke Kenneth Casson Leighton 2019-05-03 02:50:35 BST 
Hi Aleksander I moved fsqrt.py to its own subdir, it is still the same filename so use find . -name fsqrt.py ok?
Comment 8 Aleksandar Kostovic 2019-05-03 07:38:59 BST 
>Hi Aleksander I moved fsqrt.py to its own >subdir, it is still the same filename so use >find . -name fsqrt.py ok?
Thats fine. Will check it out