src/math/floorl.c

   1 /* origin: FreeBSD /usr/src/lib/msun/src/s_floorl.c */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12 /*
  13  * floorl(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 floorl(x).
  19  */
  20
  21 #include "libm.h"
  22
  23 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
  24 long double floorl(long double x)
  25 {
  26         return floor(x);
  27 }
  28 #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
  29
  30 #ifdef LDBL_IMPLICIT_NBIT
  31 #define MANH_SIZE       (LDBL_MANH_SIZE + 1)
  32 #define INC_MANH(u, c)  do {                                    \
  33         uint64_t o = u.bits.manh;                               \
  34         u.bits.manh += (c);                                     \
  35         if (u.bits.manh < o)                                    \
  36                 u.bits.exp++;                                   \
  37 } while (0)
  38 #else
  39 #define MANH_SIZE       LDBL_MANH_SIZE
  40 #define INC_MANH(u, c)  do {                                    \
  41         uint64_t o = u.bits.manh;                               \
  42         u.bits.manh += (c);                                     \
  43         if (u.bits.manh < o) {                                  \
  44                 u.bits.exp++;                                   \
  45                 u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
  46         }                                                       \
  47 } while (0)
  48 #endif
  49
  50 static const long double huge = 1.0e300;
  51
  52 long double floorl(long double x)
  53 {
  54         union IEEEl2bits u = { .e = x };
  55         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  56
  57         if (e < MANH_SIZE - 1) {
  58                 if (e < 0) {
  59                         /* raise inexact if x != 0 */
  60                         if (huge + x > 0.0)
  61                                 if (u.bits.exp > 0 ||
  62                                     (u.bits.manh | u.bits.manl) != 0)
  63                                         u.e = u.bits.sign ? -1.0 : 0.0;
  64                 } else {
  65                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  66                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  67                                 return x;  /* x is integral */
  68                         if (u.bits.sign) {
  69 #ifdef LDBL_IMPLICIT_NBIT
  70                                 if (e == 0)
  71                                         u.bits.exp++;
  72                                 else
  73 #endif
  74                                 INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
  75                         }
  76                         /* raise inexact flag */
  77                         if (huge + x > 0.0) {
  78                                 u.bits.manh &= ~m;
  79                                 u.bits.manl = 0;
  80                         }
  81                 }
  82         } else if (e < LDBL_MANT_DIG - 1) {
  83                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  84                 if ((u.bits.manl & m) == 0)
  85                         return x;  /* x is integral */
  86                 if (u.bits.sign) {
  87                         if (e == MANH_SIZE - 1)
  88                                 INC_MANH(u, 1);
  89                         else {
  90                                 uint64_t o = u.bits.manl;
  91                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  92                                 if (u.bits.manl < o)   /* got a carry */
  93                                         INC_MANH(u, 1);
  94                         }
  95                 }
  96                 /* raise inexact flag */
  97                 if (huge + x > 0.0)
  98                         u.bits.manl &= ~m;
  99         }
 100         return u.e;
 101 }
 102 #endif