lib/libm/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  * $FreeBSD: head/lib/msun/src/s_floorl.c 176280 2008-02-14 15:10:34Z bde $
  13  */
  14
  15 /*
  16  * floorl(x)
  17  * Return x rounded toward -inf to integral value
  18  * Method:
  19  *      Bit twiddling.
  20  * Exception:
  21  *      Inexact flag raised if x not equal to floorl(x).
  22  */
  23
  24 #include <float.h>
  25 #include <math.h>
  26 #include <stdint.h>
  27
  28 #include "fpmath.h"
  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
  53 floorl(long double x)
  54 {
  55         union IEEEl2bits u = { .e = x };
  56         int e = u.bits.exp - LDBL_MAX_EXP + 1;
  57
  58         if (e < MANH_SIZE - 1) {
  59                 if (e < 0) {                    /* 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                         if (huge + x > 0.0) {   /* raise inexact flag */
  77                                 u.bits.manh &= ~m;
  78                                 u.bits.manl = 0;
  79                         }
  80                 }
  81         } else if (e < LDBL_MANT_DIG - 1) {
  82                 uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
  83                 if ((u.bits.manl & m) == 0)
  84                         return (x);     /* x is integral */
  85                 if (u.bits.sign) {
  86                         if (e == MANH_SIZE - 1)
  87                                 INC_MANH(u, 1);
  88                         else {
  89                                 uint64_t o = u.bits.manl;
  90                                 u.bits.manl += 1llu << (LDBL_MANT_DIG - e - 1);
  91                                 if (u.bits.manl < o)    /* got a carry */
  92                                         INC_MANH(u, 1);
  93                         }
  94                 }
  95                 if (huge + x > 0.0)             /* raise inexact flag */
  96                         u.bits.manl &= ~m;
  97         }
  98         return (u.e);
  99 }