lib/libm/src/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 #include <sys/cdefs.h>
  15 __RCSID("$NetBSD: s_truncl.c,v 1.4 2013/11/13 12:58:11 joerg Exp $");
  16 #if 0
  17 __FBSDID("$FreeBSD: head/lib/msun/src/s_truncl.c 176280 2008-02-14 15:10:34Z bde $");
  18 #endif
  19
  20 /*
  21  * truncl(x)
  22  * Return x rounded toward 0 to integral value
  23  * Method:
  24  *      Bit twiddling.
  25  * Exception:
  26  *      Inexact flag raised if x not equal to truncl(x).
  27  */
  28 #include "namespace.h"
  29
  30 #include <float.h>
  31 #include <math.h>
  32 #include <stdint.h>
  33 #include <machine/ieee.h>
  34
  35 #ifdef __HAVE_LONG_DOUBLE
  36
  37 #ifdef __weak_alias
  38 __weak_alias(truncl, _truncl)
  39 #endif
  40
  41 #ifdef LDBL_IMPLICIT_NBIT
  42 #define MANH_SIZE       (EXT_FRACHBITS + 1)
  43 #else
  44 #define MANH_SIZE       EXT_FRACHBITS
  45 #endif
  46
  47 static const long double huge = 1.0e300;
  48 static const float zero[] = { 0.0, -0.0 };
  49
  50 long double
  51 truncl(long double x)
  52 {
  53         union ieee_ext_u ux = { .extu_ld = x, };
  54         int e = ux.extu_exp - LDBL_MAX_EXP + 1;
  55
  56         if (e < MANH_SIZE - 1) {
  57                 if (e < 0) {                    /* raise inexact if x != 0 */
  58                         if (huge + x > 0.0)
  59                                 ux.extu_ld = zero[ux.extu_sign];
  60                 } else {
  61                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  62                         if (((ux.extu_frach & m) | ux.extu_fracl) == 0)
  63                                 return (x);     /* x is integral */
  64                         if (huge + x > 0.0) {   /* raise inexact flag */
  65                                 ux.extu_frach &= ~m;
  66                                 ux.extu_fracl = 0;
  67                         }
  68                 }
  69         } else if (e < LDBL_MANT_DIG - 1) {
  70                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  71                 if ((ux.extu_fracl & m) == 0)
  72                         return (x);     /* x is integral */
  73                 if (huge + x > 0.0)             /* raise inexact flag */
  74                         ux.extu_fracl &= ~m;
  75         }
  76         return (ux.extu_ld);
  77 }
  78
  79 #endif /* __HAVE_LONG_DOUBLE */