netdev - RE: [PATCH v2 1/1] ip-link: in human readable output use dynamic precision length

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Date:	Tue, 4 Nov 2014 11:06:50 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Christian Hesse' <mail@...rm.de>,
	Stephen Hemminger <stephen@...workplumber.org>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH v2 1/1] ip-link: in human readable output use dynamic
 precision length

From: Christian Hesse
...
> diff --git a/ip/ipaddress.c b/ip/ipaddress.c
> index e240bb5..55cbc77 100644
> --- a/ip/ipaddress.c
> +++ b/ip/ipaddress.c
> @@ -324,6 +324,7 @@ static void print_num(FILE *fp, unsigned width, uint64_t count)
>  	const char *prefix = "kMGTPE";
>  	const unsigned int base = use_iec ? 1024 : 1000;
>  	uint64_t powi = 1;
> +	int precision;
>  	char buf[64];
> 
>  	if (!human_readable || count < base) {
> @@ -343,8 +344,11 @@ static void print_num(FILE *fp, unsigned width, uint64_t count)
>  		++prefix;
>  	}
> 
> -	snprintf(buf, sizeof(buf), "%.1f%c%s", (double) count / powi,
> -		 *prefix, use_iec ? "i" : "");
> +	if ((precision = 3 - snprintf(NULL, 0, "%"PRIu64, count / powi)) < 0)

Don't put assignments in conditionals.

> +		precision = 0;
> +
> +	snprintf(buf, sizeof(buf), "%.*f%c%s", precision,
> +		(double) count / powi, *prefix, use_iec ? "i" : "");
> 
>  	fprintf(fp, "%-*s ", width, buf);
>  }
> --
> 2.1.3

The above will go wrong in all sorts of horrid ways....
For instance you are doing a truncating integer divide, but the FP
value will get rounded for display.

It would be safer to use integers throughout.

Oh, and a 2Mbit E1 link is actually 2048000 :-)

	David



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