lib/msun/src/s_ceill.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_ceil.c 5.1 93/09/24
  12  */
  13
  14 #ifndef lint
  15 static char rcsid[] = "$FreeBSD$";
  16 #endif
  17
  18 /*
  19  * ceill(x)
  20  * Return x rounded toward -inf to integral value
  21  * Method:
  22  *      Bit twiddling.
  23  * Exception:
  24  *      Inexact flag raised if x not equal to ceill(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 #define INC_MANH(u, c)  do {                                    \
  36         uint64_t o = u.bits.manh;                               \
  37         u.bits.manh += (c);                                     \
  38         if (u.bits.manh < o)                                    \
  39                 u.bits.exp++;                                   \
  40 } while (0)
  41 #else
  42 #define MANH_SIZE       LDBL_MANH_SIZE
  43 #define INC_MANH(u, c)  do {                                    \
  44         uint64_t o = u.bits.manh;                               \
  45         u.bits.manh += (c);                                     \
  46         if (u.bits.manh < o) {                                  \
  47                 u.bits.exp++;                                   \
  48                 u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
  49         }                                                       \
  50 } while (0)
  51 #endif
  52
  53 static const long double huge = 1.0e300;
  54
  55 long double
  56 ceill(long double x)
  57 {
  58         union IEEEl2bits u = { .e = x };
  59         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  60
  61         if (e < MANH_SIZE - 1) {
  62                 if (e < 0) {                    /* raise inexact if x != 0 */
  63                         if (huge + x > 0.0)
  64                                 if (u.bits.exp > 0 ||
  65                                     (u.bits.manh | u.bits.manl) != 0)
  66                                         u.e = u.bits.sign ? 0.0 : 1.0;
  67                 } else {
  68                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  69                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  70                                 return (x);     /* x is integral */
  71                         if (!u.bits.sign) {
  72 #ifdef LDBL_IMPLICIT_NBIT
  73                                 if (e == 0)
  74                                         u.bits.exp++;
  75                                 else
  76 #endif
  77                                 INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
  78                         }
  79                         if (huge + x > 0.0) {   /* raise inexact flag */
  80                                 u.bits.manh &= ~m;
  81                                 u.bits.manl = 0;
  82                         }
  83                 }
  84         } else if (e < LDBL_MANT_DIG - 1) {
  85                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  86                 if ((u.bits.manl & m) == 0)
  87                         return (x);     /* x is integral */
  88                 if (!u.bits.sign) {
  89                         if (e == MANH_SIZE - 1)
  90                                 INC_MANH(u, 1);
  91                         else {
  92                                 uint64_t o = u.bits.manl;
  93                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  94                                 if (u.bits.manl < o)    /* got a carry */
  95                                         INC_MANH(u, 1);
  96                         }
  97                 }
  98                 if (huge + x > 0.0)             /* raise inexact flag */
  99                         u.bits.manl &= ~m;
 100         }
 101         return (u.e);
 102 }