nsz Git - musl/blob - src/math/s_floor.c

   1 /* @(#)s_floor.c 5.1 93/09/24 */
   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 /*
  14  * floor(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 floor(x).
  20  */
  21
  22 #include <math.h>
  23 #include "math_private.h"
  24
  25 static const double huge = 1.0e300;
  26
  27 double
  28 floor(double x)
  29 {
  30         int32_t i0,i1,j0;
  31         uint32_t i,j;
  32         EXTRACT_WORDS(i0,i1,x);
  33         j0 = ((i0>>20)&0x7ff)-0x3ff;
  34         if(j0<20) {
  35             if(j0<0) {  /* raise inexact if x != 0 */
  36                 if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
  37                     if(i0>=0) {i0=i1=0;}
  38                     else if(((i0&0x7fffffff)|i1)!=0)
  39                         { i0=0xbff00000;i1=0;}
  40                 }
  41             } else {
  42                 i = (0x000fffff)>>j0;
  43                 if(((i0&i)|i1)==0) return x; /* x is integral */
  44                 if(huge+x>0.0) {        /* raise inexact flag */
  45                     if(i0<0) i0 += (0x00100000)>>j0;
  46                     i0 &= (~i); i1=0;
  47                 }
  48             }
  49         } else if (j0>51) {
  50             if(j0==0x400) return x+x;   /* inf or NaN */
  51             else return x;              /* x is integral */
  52         } else {
  53             i = ((uint32_t)(0xffffffff))>>(j0-20);
  54             if((i1&i)==0) return x;     /* x is integral */
  55             if(huge+x>0.0) {            /* raise inexact flag */
  56                 if(i0<0) {
  57                     if(j0==20) i0+=1;
  58                     else {
  59                         j = i1+(1<<(52-j0));
  60                         if(j<i1) i0 +=1 ;       /* got a carry */
  61                         i1=j;
  62                     }
  63                 }
  64                 i1 &= (~i);
  65             }
  66         }
  67         INSERT_WORDS(x,i0,i1);
  68         return x;
  69 }