linux-kernel - Re: [PATCH 2/3] lib: vsprintf: optimised put

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Message-Id: <201008060718.38345.vda.linux@googlemail.com>
Date:	Fri, 6 Aug 2010 07:18:38 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Michal Nazarewicz <mina86@...a86.com>
Cc:	linux-kernel@...r.kernel.org, m.nazarewicz@...sung.com,
	"Douglas W. Jones" <jones@...uiowa.edu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] lib: vsprintf: optimised put_dec() for 32-bit machines

On Friday 06 August 2010 00:38, Michal Nazarewicz wrote:
> The disadvantage is that the proposed function is 2.5-3.5 bigger.
> Those are not big functions though -- we are talking here about
> proposed function being below 512.

It's a slippery slope. Here's where it ends: glibc
has memcpy() function which is "only" 8k of code or so.
I'm not joking.



> +#if BITS_PER_LONG == 64
> +
...  
> +#else
...
> +/*
> + * Based on code by Douglas W. Jones found at
> + * <http://www.cs.uiowa.edu/~jones/bcd/decimal.html#sixtyfour>.  This
> + * performs no 64-bit division and hence should be faster on 32-bit
> + * machines then the version of the function above.
> + */
> +static noinline_for_stack
> +char *put_dec(char *buf, unsigned long long n)
> +{
> +	uint32_t d3, d2, d1, q;
> +
> +	if (!n) {
> +		*buf++ = '0';
> +		return buf;
> +	}
> +
> +	d1  = (n >> 16) & 0xFFFF;
> +	d2  = (n >> 32) & 0xFFFF;
> +	d3  = (n >> 48) & 0xFFFF;

Are you assuming that sizeof(long long) == 8, always?

-- 
vda
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