src/libm/s_scalbn.c
author Ryan C. Gordon <icculus@icculus.org>
Thu, 21 Apr 2016 03:16:44 -0400
changeset 11729 d1ce8396c356
parent 11684 eccdf37f8996
child 12420 4a6c91d9cc33
permissions -rw-r--r--
Initial shot at a renderer target for Apple's Metal API.

This isn't complete, but is enough to run testsprite2. It's currently
Mac-only; with a little work to figure out how to properly glue in a Metal
layer to a UIView, this will likely work on iOS, too.

This is only wired up to the configure script right now, and disabled by
default. CMake and Xcode still need their bits filled in as appropriate.
     1 /*
     2  * ====================================================
     3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     4  *
     5  * Developed at SunPro, a Sun Microsystems, Inc. business.
     6  * Permission to use, copy, modify, and distribute this
     7  * software is freely granted, provided that this notice
     8  * is preserved.
     9  * ====================================================
    10  */
    11 
    12 /*
    13  * scalbln(double x, long n)
    14  * scalbln(x,n) returns x * 2**n computed by exponent
    15  * manipulation rather than by actually performing an
    16  * exponentiation or a multiplication.
    17  */
    18 
    19 #include "math_libm.h"
    20 #include "math_private.h"
    21 #include <limits.h>
    22 
    23 static const double
    24 two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
    25 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
    26 huge   = 1.0e+300,
    27 tiny   = 1.0e-300;
    28 
    29 double scalbln(double x, long n)
    30 {
    31 	int32_t k, hx, lx;
    32 
    33 	EXTRACT_WORDS(hx, lx, x);
    34 	k = (hx & 0x7ff00000) >> 20; /* extract exponent */
    35 	if (k == 0) { /* 0 or subnormal x */
    36 		if ((lx | (hx & 0x7fffffff)) == 0)
    37 			return x; /* +-0 */
    38 		x *= two54;
    39 		GET_HIGH_WORD(hx, x);
    40 		k = ((hx & 0x7ff00000) >> 20) - 54;
    41 	}
    42 	if (k == 0x7ff)
    43 		return x + x; /* NaN or Inf */
    44 	k = k + n;
    45 	if (k > 0x7fe)
    46 		return huge * copysign(huge, x); /* overflow */
    47 	if (n < -50000)
    48 		return tiny * copysign(tiny, x); /* underflow */
    49 	if (k > 0) { /* normal result */
    50 		SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    51 		return x;
    52 	}
    53 	if (k <= -54) {
    54 		if (n > 50000) /* in case integer overflow in n+k */
    55 			return huge * copysign(huge, x); /* overflow */
    56 		return tiny * copysign(tiny, x); /* underflow */
    57 	}
    58 	k += 54; /* subnormal result */
    59 	SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    60 	return x * twom54;
    61 }
    62 libm_hidden_def(scalbln)
    63 
    64 
    65 double scalbn(double x, int n)
    66 {
    67 	return scalbln(x, n);
    68 }
    69 libm_hidden_def(scalbn)