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
  12 /*
  13  * ceill(x)
  14  * Return x rounded toward -inf to integral value
  15  * Method:
  16  *      Bit twiddling.
  17  * Exception:
  18  *      Inexact flag raised if x not equal to ceill(x).
  19  */
  20
  21 #include <float.h>
  22 #include <math.h>
  23 #include <stdint.h>
  24
  25 #include "fpmath.h"
  26
  27 #ifdef LDBL_IMPLICIT_NBIT
  28 #define MANH_SIZE       (LDBL_MANH_SIZE + 1)
  29 #define INC_MANH(u, c)  do {                                    \
  30         uint64_t o = u.bits.manh;                               \
  31         u.bits.manh += (c);                                     \
  32         if (u.bits.manh < o)                                    \
  33                 u.bits.exp++;                                   \
  34 } while (0)
  35 #else
  36 #define MANH_SIZE       LDBL_MANH_SIZE
  37 #define INC_MANH(u, c)  do {                                    \
  38         uint64_t o = u.bits.manh;                               \
  39         u.bits.manh += (c);                                     \
  40         if (u.bits.manh < o) {                                  \
  41                 u.bits.exp++;                                   \
  42                 u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
  43         }                                                       \
  44 } while (0)
  45 #endif
  46
  47 static const long double huge = 1.0e300;
  48
  49 long double
  50 ceill(long double x)
  51 {
  52         union IEEEl2bits u = { .e = x };
  53         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  54
  55         if (e < MANH_SIZE - 1) {
  56                 if (e < 0) {                    /* raise inexact if x != 0 */
  57                         if (huge + x > 0.0)
  58                                 if (u.bits.exp > 0 ||
  59                                     (u.bits.manh | u.bits.manl) != 0)
  60                                         u.e = u.bits.sign ? -0.0 : 1.0;
  61                 } else {
  62                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  63                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  64                                 return (x);     /* x is integral */
  65                         if (!u.bits.sign) {
  66 #ifdef LDBL_IMPLICIT_NBIT
  67                                 if (e == 0)
  68                                         u.bits.exp++;
  69                                 else
  70 #endif
  71                                 INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
  72                         }
  73                         if (huge + x > 0.0) {   /* raise inexact flag */
  74                                 u.bits.manh &= ~m;
  75                                 u.bits.manl = 0;
  76                         }
  77                 }
  78         } else if (e < LDBL_MANT_DIG - 1) {
  79                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  80                 if ((u.bits.manl & m) == 0)
  81                         return (x);     /* x is integral */
  82                 if (!u.bits.sign) {
  83                         if (e == MANH_SIZE - 1)
  84                                 INC_MANH(u, 1);
  85                         else {
  86                                 uint64_t o = u.bits.manl;
  87                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  88                                 if (u.bits.manl < o)    /* got a carry */
  89                                         INC_MANH(u, 1);
  90                         }
  91                 }
  92                 if (huge + x > 0.0)             /* raise inexact flag */
  93                         u.bits.manl &= ~m;
  94         }
  95         return (u.e);
  96 }