src/libm/s_scalbn.c
author Ozkan Sezer
Thu, 29 Oct 2020 20:00:20 +0300
changeset 14209 467540bb2114
parent 13460 8bd7f8d26f83
permissions -rw-r--r--
SDL_stdinc.h: define _DARWIN_C_SOURCE on macOS for memset_pattern4()

hopefully fixes https://bugzilla.libsdl.org/show_bug.cgi?id=5107
     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 #ifdef __WATCOMC__ /* Watcom defines huge=__huge */
    24 #undef huge
    25 #endif
    26 
    27 static const double
    28 two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
    29 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
    30 huge   = 1.0e+300,
    31 tiny   = 1.0e-300;
    32 
    33 double scalbln(double x, long n)
    34 {
    35 	int32_t k, hx, lx;
    36 
    37 	EXTRACT_WORDS(hx, lx, x);
    38 	k = (hx & 0x7ff00000) >> 20; /* extract exponent */
    39 	if (k == 0) { /* 0 or subnormal x */
    40 		if ((lx | (hx & 0x7fffffff)) == 0)
    41 			return x; /* +-0 */
    42 		x *= two54;
    43 		GET_HIGH_WORD(hx, x);
    44 		k = ((hx & 0x7ff00000) >> 20) - 54;
    45 	}
    46 	if (k == 0x7ff)
    47 		return x + x; /* NaN or Inf */
    48 	k = (int32_t)(k + n);
    49 	if (k > 0x7fe)
    50 		return huge * copysign(huge, x); /* overflow */
    51 	if (n < -50000)
    52 		return tiny * copysign(tiny, x); /* underflow */
    53 	if (k > 0) { /* normal result */
    54 		SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    55 		return x;
    56 	}
    57 	if (k <= -54) {
    58 		if (n > 50000) /* in case integer overflow in n+k */
    59 			return huge * copysign(huge, x); /* overflow */
    60 		return tiny * copysign(tiny, x); /* underflow */
    61 	}
    62 	k += 54; /* subnormal result */
    63 	SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
    64 	return x * twom54;
    65 }
    66 libm_hidden_def(scalbln)
    67 
    68 
    69 double scalbn(double x, int n)
    70 {
    71 	return scalbln(x, n);
    72 }
    73 libm_hidden_def(scalbn)