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Message-ID: <20161217073600.GZ18078@example.net>
Date: Sat, 17 Dec 2016 08:36:00 +0100
From: u-uy74@...ey.se
To: musl@...ts.openwall.com
Subject: Re: [PATCH] use lookup table for malloc bin index instead of
float conversion
On Sat, Dec 17, 2016 at 12:50:58AM -0500, Rich Felker wrote:
> On Sun, Nov 27, 2016 at 03:15:41PM +0100, Szabolcs Nagy wrote:
> > +static const unsigned char bin_tab[64] = {
> > + 0, 0, 0, 0,32,33,34,35,36,36,37,37,38,38,39,39,
> > + 40,40,40,40,41,41,41,41,42,42,42,42,43,43,43,43,
> > + 44,44,44,44,44,44,44,44,45,45,45,45,45,45,45,45,
> > + 46,46,46,46,46,46,46,46,47,47,47,47,47,47,47,47,
> > +};
> > +
> > static int bin_index(size_t x)
> > {
> > x = x / SIZE_ALIGN - 1;
> > if (x <= 32) return x;
> > + if (x < 512) return bin_tab[x/8];
> > if (x > 0x1c00) return 63;
> > - return ((union { float v; uint32_t r; }){(int)x}.r>>21) - 496;
> > + return bin_tab[x/128] + 16;
> > }
> >
> > static int bin_index_up(size_t x)
> > {
> > x = x / SIZE_ALIGN - 1;
> > if (x <= 32) return x;
> > - return ((union { float v; uint32_t r; }){(int)x}.r+0x1fffff>>21) - 496;
> > + x--;
> > + if (x < 512) return bin_tab[x/8] + 1;
> > + return bin_tab[x/128] + 17;
> > }
> >
> > #if 0
> > --
> > 2.10.2
> Looks good mostly, but wouldn't it be better to drop the 4 unused
> entries from the table and add -4's to the indices?
Wouldn't this enlarge the code more than reduce the data?
Rune
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