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Re: [COMMITTED] pkl, testsuite, doc: defunit, support for arbitrary name

From: Eric Blake
Subject: Re: [COMMITTED] pkl, testsuite, doc: defunit, support for arbitrary named units
Date: Sat, 29 Feb 2020 09:23:33 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0

On 2/29/20 8:37 AM, Alfred M. Szmidt wrote:
I think following the lead of GNU Coreutils would be wise here

I agree - any time we have different GNU programs with a different set of ideas on what a suffix translates to, it breeds confusion.

defunit kB      = 10 ** 3;
# `K' is special: the SI prefix is `k' and the ISO/IEC 80000-13 prefix
# is `Ki', but tradition and POSIX use `k' to mean `KiB'.
defunit k       = 2 ** 10;
defunit K       = 2 ** 10;

Hmm - this would work for bits.

defunit KiB     = 2 ** 10;

But this, with an explicit B, is wrong (it is not 1024 bytes, but 1024 bits).

Do we want k to be kbits or kbytes?

defunit MB      = 10 ** 6;

This name implies bytes, so it should be 8 * 10 ** 6. Do we also want Mb for 1,000,000 bits?

defunit M       = 2 ** 20;

This is ambiguous on whether it means bits or bytes. Per coreutils, if we want it to mean mebibytes, we need 8 * 2 ** 20. (Yes, I avoid the term mebibytes when I can, and usually say megabytes even when I mean 2**20 rather than 10**6, but in this context, my choice of wording is intentional)

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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