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Annotation of src/lib/libc/gen/ldexp_ieee754.c, Revision 1.4.30.1

1.4.30.1! yamt        1: /*     $NetBSD: ldexp_ieee754.c,v 1.4 2003/12/30 23:19:07 martin Exp $ */
1.1       kleink      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)
1.4.30.1! yamt       34: __RCSID("$NetBSD: ldexp_ieee754.c,v 1.4 2003/12/30 23:19:07 martin Exp $");
1.1       kleink     35: #endif /* LIBC_SCCS and not lint */
                     36:
                     37: #include <sys/types.h>
                     38: #include <machine/ieee.h>
                     39: #include <errno.h>
                     40: #include <math.h>
                     41:
                     42: /*
                     43:  * Multiply the given value by 2^expon.
                     44:  */
                     45: double
                     46: ldexp(double val, int expon)
                     47: {
                     48:        int oldexp, newexp;
1.2       kleink     49:        union ieee_double_u u, mul;
1.1       kleink     50:
1.3       mrg        51:        u.dblu_d = val;
1.2       kleink     52:        oldexp = u.dblu_dbl.dbl_exp;
1.1       kleink     53:
                     54:        /*
                     55:         * If input is zero, Inf or NaN, just return it.
                     56:         */
1.2       kleink     57:        if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN)
1.1       kleink     58:                return (val);
                     59:
                     60:        if (oldexp == 0) {
                     61:                /*
                     62:                 * u.v is denormal.  We must adjust it so that the exponent
                     63:                 * arithmetic below will work.
                     64:                 */
                     65:                if (expon <= DBL_EXP_BIAS) {
                     66:                        /*
                     67:                         * Optimization: if the scaling can be done in a single
                     68:                         * multiply, or underflows, just do it now.
                     69:                         */
                     70:                        if (expon <= -DBL_FRACBITS) {
                     71:                                errno = ERANGE;
1.4       martin     72:                                return (val < 0.0 ? -0.0 : 0.0);
1.1       kleink     73:                        }
1.2       kleink     74:                        mul.dblu_d = 0.0;
                     75:                        mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
                     76:                        u.dblu_d *= mul.dblu_d;
                     77:                        if (u.dblu_d == 0.0) {
1.1       kleink     78:                                errno = ERANGE;
1.4       martin     79:                                return (val < 0.0 ? -0.0 : 0.0);
1.1       kleink     80:                        }
1.2       kleink     81:                        return (u.dblu_d);
1.1       kleink     82:                } else {
                     83:                        /*
                     84:                         * We know that expon is very large, and therefore the
                     85:                         * result cannot be denormal (though it may be Inf).
                     86:                         * Shift u.v by just enough to make it normal.
                     87:                         */
1.2       kleink     88:                        mul.dblu_d = 0.0;
                     89:                        mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
                     90:                        u.dblu_d *= mul.dblu_d;
1.1       kleink     91:                        expon -= DBL_FRACBITS;
1.2       kleink     92:                        oldexp = u.dblu_dbl.dbl_exp;
1.1       kleink     93:                }
                     94:        }
                     95:
                     96:        /*
                     97:         * u.v is now normalized and oldexp has been adjusted if necessary.
                     98:         * Calculate the new exponent and check for underflow and overflow.
                     99:         */
                    100:        newexp = oldexp + expon;
                    101:
                    102:        if (newexp <= 0) {
                    103:                /*
                    104:                 * The output number is either denormal or underflows (see
                    105:                 * comments in machine/ieee.h).
                    106:                 */
                    107:                if (newexp <= -DBL_FRACBITS) {
                    108:                        errno = ERANGE;
1.4       martin    109:                        return (val < 0.0 ? -0.0 : 0.0);
1.1       kleink    110:                }
                    111:                /*
                    112:                 * Denormalize the result.  We do this with a multiply.  If
                    113:                 * expon is very large, it won't fit in a double, so we have
                    114:                 * to adjust the exponent first.  This is safe because we know
                    115:                 * that u.v is normal at this point.
                    116:                 */
                    117:                if (expon <= -DBL_EXP_BIAS) {
1.2       kleink    118:                        u.dblu_dbl.dbl_exp = 1;
1.1       kleink    119:                        expon += oldexp - 1;
                    120:                }
1.2       kleink    121:                mul.dblu_d = 0.0;
                    122:                mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
                    123:                u.dblu_d *= mul.dblu_d;
                    124:                return (u.dblu_d);
1.1       kleink    125:        } else if (newexp >= DBL_EXP_INFNAN) {
                    126:                /*
                    127:                 * The result overflowed; return +/-Inf.
                    128:                 */
1.2       kleink    129:                u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN;
                    130:                u.dblu_dbl.dbl_frach = 0;
                    131:                u.dblu_dbl.dbl_fracl = 0;
1.1       kleink    132:                errno = ERANGE;
1.2       kleink    133:                return (u.dblu_d);
1.1       kleink    134:        } else {
                    135:                /*
                    136:                 * The result is normal; just replace the old exponent with the
                    137:                 * new one.
                    138:                 */
1.2       kleink    139:                u.dblu_dbl.dbl_exp = newexp;
                    140:                return (u.dblu_d);
1.1       kleink    141:        }
                    142: }

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