Date: Sun, 12 Aug 2012 22:58:22 -0000 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: Peter Jeremy <peter@rulingia.com> 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>, Bruce Evans <brde@optusnet.com.au>, David Schultz <das@freebsd.org>, Warner Losh <imp@bsdimp.com> Subject: Re: Use of C99 extra long double math functions after r236148 Message-ID: <20120719234425.GA6280@troutmask.apl.washington.edu> Resent-Message-ID: <20120812225815.GM20453@server.rulingia.com> In-Reply-To: <20120719213944.GA21199@server.rulingia.com> References: <5004A5C7.1040405@missouri.edu> <5004DEA9.1050001@missouri.edu> <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>
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On Fri, Jul 20, 2012 at 07:39:44AM +1000, Peter Jeremy wrote:
> On 2012-Jul-18 14:01:42 +1000, Bruce Evans <brde@optusnet.com.au> wrote:
>
> >The standard classification macros are good for developing things, but
> >they are very slow. All (?) committed complex functions use hard-coded
> >bit test.
>
> I notice that the functions are full of hard-coded magic constants.
> Would these be better as macros to:
> 1) Provide a description as to their purpose; and
> 2) Reduce differences between the float/long/double function bodies?
>
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;
/* high word of |x| */
hx &= 0x7fffffff;
/* NaN */
if (hx > 0x7f800000)
return (x + x);
/* exp(+-inf) = {inf, 0} */
if (hx == 0x7f800000)
return (xsb == 0) ? x : 0.0;
/* subnormal */
if (hx < 0x00800000)
Idioms used in lib with double type:
u_int32_t hx, lx, xsb
EXTRACT_WORDS(hx, lx, x);
/* sign bit of x */
xsb = (hx >> 31) & 1;
/* high word of |x| */
hx &= 0x7fffffff;
/* subnormal */
if (hx < 0x00100000)
/* Test for NaN and +-Inf. */
if (hx >= 0x7ff00000) {
/* Is it a NaN? */
if (((hx & 0xfffff) | lx) != 0)
return (x + x);
/* It's an +-Inf. */
return ((xsb == 0) ? x : 0.0); /* exp(+-inf)={inf,0} */
}
--
Steve
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