Home | History | Annotate | Line # | Download | only in gen
compat_ldexp_ieee754.c revision 1.6 
      1 /* $NetBSD: compat_ldexp_ieee754.c,v 1.6 2016/08/27 09:11:56 christos Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 1999 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Charles M. Hannum.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 #if defined(LIBC_SCCS) && !defined(lint)
     34 __RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.6 2016/08/27 09:11:56 christos Exp $");
     35 #endif /* LIBC_SCCS and not lint */
     36 
     37 #include <sys/types.h>
     38 #include <machine/ieee.h>
     39 #include <errno.h>
     40 
     41 double ldexp(double, int);
     42 
     43 #include <stdio.h>
     44 /*
     45  * Multiply the given value by 2^expon.
     46  */
     47 double
     48 ldexp(double val, int expon)
     49 {
     50 	int oldexp, newexp;
     51 	union ieee_double_u u, mul;
     52 
     53 	u.dblu_d = val;
     54 	oldexp = u.dblu_dbl.dbl_exp;
     55 
     56 	/*
     57 	 * If input is zero, Inf or NaN, just return it.
     58 	 */
     59 	if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN)
     60 		return (val);
     61 
     62 	if (oldexp == 0) {
     63 		/*
     64 		 * u.v is denormal.  We must adjust it so that the exponent
     65 		 * arithmetic below will work.
     66 		 */
     67 		if (expon <= DBL_EXP_BIAS) {
     68 			/*
     69 			 * Optimization: if the scaling can be done in a single
     70 			 * multiply, or underflows, just do it now.
     71 			 */
     72 			if (expon <= -DBL_FRACBITS) {
     73 				errno = ERANGE;
     74 				return (val < 0.0 ? -0.0 : 0.0);
     75 			}
     76 			mul.dblu_d = 0.0;
     77 			mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
     78 			u.dblu_d *= mul.dblu_d;
     79 			if (u.dblu_d == 0.0) {
     80 				errno = ERANGE;
     81 				return (val < 0.0 ? -0.0 : 0.0);
     82 			}
     83 			return (u.dblu_d);
     84 		} else {
     85 			/*
     86 			 * We know that expon is very large, and therefore the
     87 			 * result cannot be denormal (though it may be Inf).
     88 			 * Shift u.v by just enough to make it normal.
     89 			 */
     90 			mul.dblu_d = 0.0;
     91 			mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
     92 			u.dblu_d *= mul.dblu_d;
     93 			expon -= DBL_FRACBITS;
     94 			oldexp = u.dblu_dbl.dbl_exp;
     95 		}
     96 	}
     97 
     98 	/*
     99 	 * u.v is now normalized and oldexp has been adjusted if necessary.
    100 	 * Calculate the new exponent and check for underflow and overflow.
    101 	 */
    102 	newexp = oldexp + expon;
    103 	printf("ee %#x oldexp %#x\n", oldexp, expon);
    104 
    105 	if (newexp >= DBL_EXP_INFNAN ||
    106 	    (oldexp >= 0 && expon >= DBL_EXP_INFNAN)) {
    107 		/*
    108 		 * The result overflowed; return +/-Inf.
    109 		 */
    110 		u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN;
    111 		u.dblu_dbl.dbl_frach = 0;
    112 		u.dblu_dbl.dbl_fracl = 0;
    113 		errno = ERANGE;
    114 		return (u.dblu_d);
    115 	} else if (newexp <= 0) {
    116 		/*
    117 		 * The output number is either denormal or underflows (see
    118 		 * comments in machine/ieee.h).
    119 		 */
    120 		if (newexp <= -DBL_FRACBITS) {
    121 			errno = ERANGE;
    122 			return (val < 0.0 ? -0.0 : 0.0);
    123 		}
    124 		/*
    125 		 * Denormalize the result.  We do this with a multiply.  If
    126 		 * expon is very large, it won't fit in a double, so we have
    127 		 * to adjust the exponent first.  This is safe because we know
    128 		 * that u.v is normal at this point.
    129 		 */
    130 		if (expon <= -DBL_EXP_BIAS) {
    131 			u.dblu_dbl.dbl_exp = 1;
    132 			expon += oldexp - 1;
    133 		}
    134 		mul.dblu_d = 0.0;
    135 		mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
    136 		u.dblu_d *= mul.dblu_d;
    137 		return (u.dblu_d);
    138 	} else {
    139 		/*
    140 		 * The result is normal; just replace the old exponent with the
    141 		 * new one.
    142 		 */
    143 		u.dblu_dbl.dbl_exp = newexp;
    144 		return (u.dblu_d);
    145 	}
    146 }
    147