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 #include <sys/cdefs.h>
  13 /*
  14  * ceill(x)
  15  * Return x rounded toward -inf to integral value
  16  * Method:
  17  *      Bit twiddling.
  18  * Exception:
  19  *      Inexact flag raised if x not equal to ceill(x).
  20  */
  21
  22 #include <float.h>
  23 #include <math.h>
  24 #include <stdint.h>
  25
  26 #include "fpmath.h"
  27
  28 #ifdef LDBL_IMPLICIT_NBIT
  29 #define MANH_SIZE       (LDBL_MANH_SIZE + 1)
  30 #define INC_MANH(u, c)  do {                                    \
  31         uint64_t o = u.bits.manh;                               \
  32         u.bits.manh += (c);                                     \
  33         if (u.bits.manh < o)                                    \
  34                 u.bits.exp++;                                   \
  35 } while (0)
  36 #else
  37 #define MANH_SIZE       LDBL_MANH_SIZE
  38 #define INC_MANH(u, c)  do {                                    \
  39         uint64_t o = u.bits.manh;                               \
  40         u.bits.manh += (c);                                     \
  41         if (u.bits.manh < o) {                                  \
  42                 u.bits.exp++;                                   \
  43                 u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
  44         }                                                       \
  45 } while (0)
  46 #endif
  47
  48 static const long double huge = 1.0e300;
  49
  50 long double
  51 ceill(long double x)
  52 {
  53         union IEEEl2bits u = { .e = x };
  54         int e = u.bits.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                                 if (u.bits.exp > 0 ||
  60                                     (u.bits.manh | u.bits.manl) != 0)
  61                                         u.e = u.bits.sign ? -0.0 : 1.0;
  62                 } else {
  63                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  64                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  65                                 return (x);     /* x is integral */
  66                         if (!u.bits.sign) {
  67 #ifdef LDBL_IMPLICIT_NBIT
  68                                 if (e == 0)
  69                                         u.bits.exp++;
  70                                 else
  71 #endif
  72                                 INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
  73                         }
  74                         if (huge + x > 0.0) {   /* raise inexact flag */
  75                                 u.bits.manh &= ~m;
  76                                 u.bits.manl = 0;
  77                         }
  78                 }
  79         } else if (e < LDBL_MANT_DIG - 1) {
  80                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  81                 if ((u.bits.manl & m) == 0)
  82                         return (x);     /* x is integral */
  83                 if (!u.bits.sign) {
  84                         if (e == MANH_SIZE - 1)
  85                                 INC_MANH(u, 1);
  86                         else {
  87                                 uint64_t o = u.bits.manl;
  88                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  89                                 if (u.bits.manl < o)    /* got a carry */
  90                                         INC_MANH(u, 1);
  91                         }
  92                 }
  93                 if (huge + x > 0.0)             /* raise inexact flag */
  94                         u.bits.manl &= ~m;
  95         }
  96         return (u.e);
  97 }