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Date:      Sun, 12 Aug 2012 22:58:35 -0000
From:      Steve Kargl <sgk@troutmask.apl.washington.edu>
To:        Bruce Evans <brde@optusnet.com.au>
Cc:        Diane Bruce <db@db.net>, John Baldwin <jhb@freebsd.org>, David Chisnall <theraven@freebsd.org>, Stephen Montgomery-Smith <stephen@missouri.edu>, Bruce Evans <bde@freebsd.org>, David Schultz <das@freebsd.org>, Peter Jeremy <peter@rulingia.com>, Warner Losh <imp@bsdimp.com>
Subject:   Re: Use of C99 extra long double math functions after r236148
Message-ID:  <20120720043004.GA7404@troutmask.apl.washington.edu>
Resent-Message-ID: <20120812225828.GO20453@server.rulingia.com>
In-Reply-To: <20120720130309.P814@besplex.bde.org>
References:  <20120717040118.GA86840@troutmask.apl.washington.edu> <20120717042125.GF66913@server.rulingia.com> <20120717043848.GB87001@troutmask.apl.washington.edu> <20120717225328.GA86902@server.rulingia.com> <20120717232740.GA95026@troutmask.apl.washington.edu> <20120718001337.GA87817@server.rulingia.com> <20120718123627.D1575@besplex.bde.org> <20120719213944.GA21199@server.rulingia.com> <20120719234425.GA6280@troutmask.apl.washington.edu> <20120720130309.P814@besplex.bde.org>

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On Fri, Jul 20, 2012 at 02:12:20PM +1000, Bruce Evans wrote:
> On Thu, 19 Jul 2012, Steve Kargl wrote:
> 
> >I collected some of the float and double into a cheat sheet.
> >
> >Idioms used in libm with float type:
> >
> > int32_t xsb;
> > u_int32_t hx;
> >
> > GET_FLOAT_WORD(hx, x);
> >
> > /* Get the sign bit of x */
> > xsb = (hx >> 31) & 1;
> 
> Getting it without shifting it (hx & 0x8000) is more efficient and common.
> You don't need to shift it in this example.

I collected these from msun/src, when I was trying to understand
the magic numbers.  I suppose someone should audit the code for
consistency. :-)

laptop:kargl[219] grep " (hx>>31)&1" *c
e_exp.c:        xsb = (hx>>31)&1;               /* sign bit of x */
e_expf.c:       xsb = (hx>>31)&1;               /* sign bit of x */

-- 
Steve



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