compiler/mlib/s_truncl.c

   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  * From: @(#)s_floor.c 5.1 93/09/24
  12  */
  13
  14 #ifndef lint
  15 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_truncl.c,v 1.4 2005/04/28 19:45:55 stefanf Exp $";
  16 #endif
  17
  18 /*
  19  * truncl(x)
  20  * Return x rounded toward 0 to integral value
  21  * Method:
  22  *      Bit twiddling.
  23  * Exception:
  24  *      Inexact flag raised if x not equal to truncl(x).
  25  */
  26
  27 #include <float.h>
  28 #include <math.h>
  29 #include <stdint.h>
  30
  31 #include "fpmath.h"
  32
  33 #ifdef LDBL_IMPLICIT_NBIT
  34 #define MANH_SIZE       (LDBL_MANH_SIZE + 1)
  35 #else
  36 #define MANH_SIZE       LDBL_MANH_SIZE
  37 #endif
  38
  39 static const long double huge = 1.0e300;
  40
  41 long double
  42 truncl(long double x)
  43 {
  44         union IEEEl2bits u = { .e = x };
  45         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  46
  47         if (e < MANH_SIZE - 1) {
  48                 if (e < 0) {                    /* raise inexact if x != 0 */
  49                         if (huge + x > 0.0)
  50                                 u.e = 0.0;
  51                 } else {
  52                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  53                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  54                                 return (x);     /* x is integral */
  55                         if (huge + x > 0.0) {   /* raise inexact flag */
  56                                 u.bits.manh &= ~m;
  57                                 u.bits.manl = 0;
  58                         }
  59                 }
  60         } else if (e < LDBL_MANT_DIG - 1) {
  61                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  62                 if ((u.bits.manl & m) == 0)
  63                         return (x);     /* x is integral */
  64                 if (huge + x > 0.0)             /* raise inexact flag */
  65                         u.bits.manl &= ~m;
  66         }
  67         return (u.e);
  68 }