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Message-ID: <1445938473.6332.17.camel@linux.intel.com>
Subject: Re: [PATCH 2/3] lib/string_helpers.c: don't lose precision in
 string_get_size()
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        James Bottomley <JBottomley@Odin.com>,
        Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Date: Tue, 27 Oct 2015 11:34:33 +0200
In-Reply-To: <87fv0wyah4.fsf@vitty.brq.redhat.com>
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On Tue, 2015-10-27 at 09:36 +0100, Vitaly Kuznetsov wrote:
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> 
> > On Mon, 2015-10-26 at 14:55 +0100, Vitaly Kuznetsov wrote:
> > > string_get_size() loses precision when there is a remainder for
> > > blk_size / divisor[units] and size is big enough. E.g
> > > string_get_size(8192, 4096, STRING_UNITS_10, ...) returns "32.7
> > > MB"
> > > while it is supposed to return "33.5 MB". For some artificial
> > > inputs
> > > the result can be ridiculously wrong, e.g.
> > > string_get_size(3000, 1900, STRING_UNITS_10, ...) returns "3.00
> > > MB"
> > > when "5.70 MB" is expected.

[]

> > > -	int i, j;
> > > -	u32 remainder = 0, sf_cap, exp;
> > > +	int order = 0, j;
> > > +	u64 remainder = 0;
> > > +	u32 sf_cap;
> > >  	char tmp[8];
> > >  	const char *unit;
> > >  
> > >  	tmp[0] = '\0';
> > > -	i = 0;
> > 
> > Maybe leave i naming as is. Your order is not strictly speaking an
> > order, rather 3x order. I will make patch neater.
> > 
> 
> While reading the original function I found meaningless 'i' and 'j'
> here
> a bit consufing but yes, strictly speaking 'i' is a power of
> divisor[units], not 'order' and I don't have a good name for it
> (div_power?). I'll revert back to 'i' in v2.

I agree that names suck, however it might be better to have separate
patch to fix naming.

Rasmus?

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy