linux-kernel - Re: [RFCv3][PATCH 1/4] replace string_get

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Date:	Sat, 01 Oct 2011 12:29:19 -0700
From:	Joe Perches <joe@...ches.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	rientjes@...gle.com, James.Bottomley@...senPartnership.com,
	hpa@...or.com
Subject: Re: [RFCv3][PATCH 1/4] replace string_get_size() arrays

On Fri, 2011-09-30 at 17:08 -0700, Dave Hansen wrote:
> Instead of explicitly storing the entire string for each
> possible units, just store the thing that varies: the
> first character.

trivia

> diff -puN lib/string_helpers.c~string_get_size-pow2 lib/string_helpers.c
> --- linux-2.6.git/lib/string_helpers.c~string_get_size-pow2	2011-09-30 16:50:31.628981352 -0700
> +++ linux-2.6.git-dave/lib/string_helpers.c	2011-09-30 17:04:02.211607364 -0700
> @@ -8,6 +8,23 @@
>  #include <linux/module.h>
>  #include <linux/string_helpers.h>
>  
> +static const char byte_units[] = "_KMGTPEZY";

u64 could be up to ~1.8**19 decimal
zetta and yotta are not possible or necessary.
u128 maybe someday, but then other changes
would be necessary.

> +static char *__units_str(enum string_size_units unit, char *buf, int index)
> +{
> +	int place = 0;
> +
> +	/* index=0 is plain 'B' with no other unit */
> +	if (index) {
> +		buf[place++] = byte_units[index];

unbounded index (doesn't matter currently, it will for u128)

> @@ -23,26 +40,19 @@
>  int string_get_size(u64 size, const enum string_size_units units,
>  		    char *buf, int len)
[]
>  	const unsigned int divisor[] = {
>  		[STRING_UNITS_10] = 1000,
>  		[STRING_UNITS_2] = 1024,
>  	};

static const or it might be better to use
as that would make the code clearer.

	unsigned int divisor = (string_size_units == STRING_UNITS_2) ? 1024 : 1000;

> @@ -61,7 +71,7 @@ int string_get_size(u64 size, const enum
>  	}
>  
>  	snprintf(buf, len, "%lld%s %s", (unsigned long long)size,

%llu

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