lib/libm/src/s_modfl.c

   1 /*-
   2  * Copyright (c) 2007 David Schultz <das@FreeBSD.ORG>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * Derived from s_modf.c, which has the following Copyright:
  27  * ====================================================
  28  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  29  *
  30  * Developed at SunPro, a Sun Microsystems, Inc. business.
  31  * Permission to use, copy, modify, and distribute this
  32  * software is freely granted, provided that this notice
  33  * is preserved.
  34  * ====================================================
  35  *
  36  * $FreeBSD: head/lib/msun/src/s_modfl.c 165855 2007-01-07 07:54:21Z das $
  37  */
  38 #include <sys/cdefs.h>
  39 __RCSID("$NetBSD: s_modfl.c,v 1.1 2014/06/16 12:54:43 joerg Exp $");
  40
  41 #include "namespace.h"
  42
  43 #include <float.h>
  44 #include <math.h>
  45 #include <stdint.h>
  46 #include <machine/ieee.h>
  47
  48 #ifdef __HAVE_LONG_DOUBLE
  49
  50 #ifdef __weak_alias
  51 __weak_alias(modfl, _modfl)
  52 #endif
  53
  54 #if LDBL_MANL_SIZE > 32
  55 #define MASK    ((uint64_t)-1)
  56 #else
  57 #define MASK    ((uint32_t)-1)
  58 #endif
  59 /* Return the last n bits of a word, representing the fractional part. */
  60 #define GETFRAC(bits, n)        ((bits) & ~(MASK << (n)))
  61 /* The number of fraction bits in manh, not counting the integer bit */
  62 #define HIBITS  (LDBL_MANT_DIG - EXT_FRACHBITS)
  63
  64 static const long double zero[] = { 0.0L, -0.0L };
  65
  66 long double
  67 modfl(long double x, long double *iptr)
  68 {
  69         union ieee_ext_u ux = { .extu_ld = x, };
  70         int e = ux.extu_exp - LDBL_MAX_EXP + 1;
  71
  72         if (e < HIBITS) {                       /* Integer part is in manh. */
  73                 if (e < 0) {                    /* |x|<1 */
  74                         *iptr = zero[ux.extu_sign];
  75                         return (x);
  76                 } else {
  77                         if ((GETFRAC(ux.extu_frach, HIBITS - 1 - e) |
  78                              ux.extu_fracl) == 0) {     /* X is an integer. */
  79                                 *iptr = x;
  80                                 return (zero[ux.extu_sign]);
  81                         } else {
  82                                 /* Clear all but the top e+1 bits. */
  83                                 ux.extu_frach >>= HIBITS - 1 - e;
  84                                 ux.extu_frach <<= HIBITS - 1 - e;
  85                                 ux.extu_fracl = 0;
  86                                 *iptr = ux.extu_ld;
  87                                 return (x - ux.extu_ld);
  88                         }
  89                 }
  90         } else if (e >= LDBL_MANT_DIG - 1) {    /* x has no fraction part. */
  91                 *iptr = x;
  92                 if (x != x)                     /* Handle NaNs. */
  93                         return (x);
  94                 return (zero[ux.extu_sign]);
  95         } else {                                /* Fraction part is in manl. */
  96                 if (GETFRAC(ux.extu_fracl, LDBL_MANT_DIG - 1 - e) == 0) {
  97                         /* x is integral. */
  98                         *iptr = x;
  99                         return (zero[ux.extu_sign]);
 100                 } else {
 101                         /* Clear all but the top e+1 bits. */
 102                         ux.extu_fracl >>= LDBL_MANT_DIG - 1 - e;
 103                         ux.extu_fracl <<= LDBL_MANT_DIG - 1 - e;
 104                         *iptr = ux.extu_ld;
 105                         return (x - ux.extu_ld);
 106                 }
 107         }
 108 }
 109 #endif /* __HAVE_LONG_DOUBLE */