[Toybox] [PATCH] Add support for 1024 as well as 1000 to human_readable.

[James McMechan]

> Date: Mon, 24 Aug 2015 20:47:03 -0500
> From: rob at landley.net
> To: enh at google.com
> CC: toybox at lists.landley.net
> Subject: Re: [Toybox] [PATCH] Add support for 1024 as well as 1000 to human_readable.
>
> On 08/24/2015 03:10 PM, enh wrote:
>> On Sun, Aug 23, 2015 at 6:20 PM, Rob Landley <rob at landley.net> wrote:
>>> /me wists for a specification. Oh well. I hate when I have to guess at
>>> what the right behavior _is_...

Well checking back with my copy of "Engineering Fundamentals and Problem Solving" A. Eide et al 1979 Ch 5
Engineering units are 0.1 to 999 followed by a space, prefix and SI unit.

I am of the opinion that gratious loss of precision should be avoided.
Since a one chararacter prefix and decimal point take two character spaces the natural
breakpoint would be 10000 e.g. 9998,9999,10 k for SI decimal notation.
Using the IEC two character binary prefix Ki/Mi/Gi uses three spaces with the '.'
This would however yeild a breakpoint at 100 000 or 10 000 if we use a thousands seperator.
Which seems to me a bit large.

>> yeah, i was actually trying to avoid ending up with all the heuristics
>> the BSD implementation has.
>>
>> the BSD man page says:
>>
>> If the formatted number (including suffix) would be too long to fit into
>> buf, then divide number by 1024 until it will.
>
> That's just "test against 999, divide by 1024". Easy enough.
>
>> The len argument must be at least 4 plus the length of suffix, in order
>> to ensure a useful result is generated into buf.
>
> That constraint's already implicit. I should make sure it's explicit.
>
>> so it certainly seems they follow the "no more than three digits/two
>> digits plus '.'" rule.
>
> I can work with this.
>
> Thanks,
>
> Rob

Attached is a patch that should allow for 0..9999, 10 k..999 k, 1.0 M..999 M SI units
0..9999, 9.8 Ki..999 Ki, 1.0 Mi..999 Mi... IEC binary units, note the 9999 -> 9.8 Ki transition
I have tested this with LE32 BE32 LE64 while I have BE64 sparc I do not have a BE64 userspace
and my other BE64 system is still on order.

You can also set a flags to drop the space between number and prefix or use the ubuntu 0..1023 style
also you can request the limited range 0..999, 1.0 k-999 k style in either SI or IEC

This is  pure integer, I could open code the printf also as it can only have 4 digits maximum at the moment.
If you want I could make it autosizing rather than just one decimal between 0.1..9.9
Also if any of the symbols are defined to 0 the capability will drop out.
Perhaps I should make it default to IEC "Ki" style? getting it right vs bug compatibility.

I made a testing command e.g. toybox_human_readable_test to allow me to test it.

I hope this is interesting.

Jim McMechan
 		 	   		  
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