newlib/libm/ld/s_modfl.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  *
  28  * Derived from s_modf.c, which has the following Copyright:
  29  * ====================================================
  30  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  31  *
  32  * Developed at SunPro, a Sun Microsystems, Inc. business.
  33  * Permission to use, copy, modify, and distribute this
  34  * software is freely granted, provided that this notice
  35  * is preserved.
  36  * ====================================================
  37  *
  38  * $FreeBSD$
  39  */
  40
  41 #include <float.h>
  42 #include <math.h>
  43 #include <sys/types.h>
  44
  45 #include "fpmath.h"
  46
  47 #if LDBL_MANL_SIZE > 32
  48 #define MASK    ((uint64_t)-1)
  49 #else
  50 #define MASK    ((uint32_t)-1)
  51 #endif
  52 /* Return the last n bits of a word, representing the fractional part. */
  53 #define GETFRAC(bits, n)        ((bits) & ~(MASK << (n)))
  54 /* The number of fraction bits in manh, not counting the integer bit */
  55 #define HIBITS  (LDBL_MANT_DIG - LDBL_MANL_SIZE)
  56
  57 static const long double zero[] = { 0.0L, -0.0L };
  58
  59 long double
  60 modfl(long double x, long double *iptr)
  61 {
  62         union IEEEl2bits ux;
  63         int e;
  64
  65         ux.e = x;
  66         e = ux.bits.exp - LDBL_MAX_EXP + 1;
  67         if (e < HIBITS) {                       /* Integer part is in manh. */
  68                 if (e < 0) {                    /* |x|<1 */
  69                         *iptr = zero[ux.bits.sign];
  70                         return (x);
  71                 } else {
  72                         if ((GETFRAC(ux.bits.manh, HIBITS - 1 - e) |
  73                              ux.bits.manl) == 0) {      /* X is an integer. */
  74                                 *iptr = x;
  75                                 return (zero[ux.bits.sign]);
  76                         } else {
  77                                 /* Clear all but the top e+1 bits. */
  78                                 ux.bits.manh >>= HIBITS - 1 - e;
  79                                 ux.bits.manh <<= HIBITS - 1 - e;
  80                                 ux.bits.manl = 0;
  81                                 *iptr = ux.e;
  82                                 return (x - ux.e);
  83                         }
  84                 }
  85         } else if (e >= LDBL_MANT_DIG - 1) {    /* x has no fraction part. */
  86                 *iptr = x;
  87                 if (x != x)                     /* Handle NaNs. */
  88                         return (x);
  89                 return (zero[ux.bits.sign]);
  90         } else {                                /* Fraction part is in manl. */
  91                 if (GETFRAC(ux.bits.manl, LDBL_MANT_DIG - 1 - e) == 0) {
  92                         /* x is integral. */
  93                         *iptr = x;
  94                         return (zero[ux.bits.sign]);
  95                 } else {
  96                         /* Clear all but the top e+1 bits. */
  97                         ux.bits.manl >>= LDBL_MANT_DIG - 1 - e;
  98                         ux.bits.manl <<= LDBL_MANT_DIG - 1 - e;
  99                         *iptr = ux.e;
 100                         return (x - ux.e);
 101                 }
 102         }
 103 }