lib/msun/src/s_floorl.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 __FBSDID("$FreeBSD$");
  16
  17 /*
  18  * floorl(x)
  19  * Return x rounded toward -inf to integral value
  20  * Method:
  21  *      Bit twiddling.
  22  * Exception:
  23  *      Inexact flag raised if x not equal to floorl(x).
  24  */
  25
  26 #include <float.h>
  27 #include <math.h>
  28 #include <stdint.h>
  29
  30 #include "fpmath.h"
  31
  32 #ifdef LDBL_IMPLICIT_NBIT
  33 #define MANH_SIZE       (LDBL_MANH_SIZE + 1)
  34 #define INC_MANH(u, c)  do {                                    \
  35         uint64_t o = u.bits.manh;                               \
  36         u.bits.manh += (c);                                     \
  37         if (u.bits.manh < o)                                    \
  38                 u.bits.exp++;                                   \
  39 } while (0)
  40 #else
  41 #define MANH_SIZE       LDBL_MANH_SIZE
  42 #define INC_MANH(u, c)  do {                                    \
  43         uint64_t o = u.bits.manh;                               \
  44         u.bits.manh += (c);                                     \
  45         if (u.bits.manh < o) {                                  \
  46                 u.bits.exp++;                                   \
  47                 u.bits.manh |= 1llu << (LDBL_MANH_SIZE - 1);    \
  48         }                                                       \
  49 } while (0)
  50 #endif
  51
  52 static const long double huge = 1.0e300;
  53
  54 long double
  55 floorl(long double x)
  56 {
  57         union IEEEl2bits u = { .e = x };
  58         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  59
  60         if (e < MANH_SIZE - 1) {
  61                 if (e < 0) {                    /* raise inexact if x != 0 */
  62                         if (huge + x > 0.0)
  63                                 if (u.bits.exp > 0 ||
  64                                     (u.bits.manh | u.bits.manl) != 0)
  65                                         u.e = u.bits.sign ? -1.0 : 0.0;
  66                 } else {
  67                         uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
  68                         if (((u.bits.manh & m) | u.bits.manl) == 0)
  69                                 return (x);     /* x is integral */
  70                         if (u.bits.sign) {
  71 #ifdef LDBL_IMPLICIT_NBIT
  72                                 if (e == 0)
  73                                         u.bits.exp++;
  74                                 else
  75 #endif
  76                                 INC_MANH(u, 1llu << (MANH_SIZE - e - 1));
  77                         }
  78                         if (huge + x > 0.0) {   /* raise inexact flag */
  79                                 u.bits.manh &= ~m;
  80                                 u.bits.manl = 0;
  81                         }
  82                 }
  83         } else if (e < LDBL_MANT_DIG - 1) {
  84                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  85                 if ((u.bits.manl & m) == 0)
  86                         return (x);     /* x is integral */
  87                 if (u.bits.sign) {
  88                         if (e == MANH_SIZE - 1)
  89                                 INC_MANH(u, 1);
  90                         else {
  91                                 uint64_t o = u.bits.manl;
  92                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  93                                 if (u.bits.manl < o)    /* got a carry */
  94                                         INC_MANH(u, 1);
  95                         }
  96                 }
  97                 if (huge + x > 0.0)             /* raise inexact flag */
  98                         u.bits.manl &= ~m;
  99         }
 100         return (u.e);
 101 }