SDL  2.0
s_floor.c
Go to the documentation of this file.
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 /*
13  * floor(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 floor(x).
19  */
20 
21 /*#include <features.h>*/
22 /* Prevent math.h from defining a colliding inline */
23 #undef __USE_EXTERN_INLINES
24 #include "math_libm.h"
25 #include "math_private.h"
26 
27 static const double huge = 1.0e300;
28 
29 double floor(double x)
30 {
31  int32_t i0,i1,j0;
32  u_int32_t i,j;
33  EXTRACT_WORDS(i0,i1,x);
34  j0 = ((i0>>20)&0x7ff)-0x3ff;
35  if(j0<20) {
36  if(j0<0) { /* raise inexact if x != 0 */
37  if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
38  if(i0>=0) {i0=i1=0;}
39  else if(((i0&0x7fffffff)|i1)!=0)
40  { i0=0xbff00000;i1=0;}
41  }
42  } else {
43  i = (0x000fffff)>>j0;
44  if(((i0&i)|i1)==0) return x; /* x is integral */
45  if(huge+x>0.0) { /* raise inexact flag */
46  if(i0<0) i0 += (0x00100000)>>j0;
47  i0 &= (~i); i1=0;
48  }
49  }
50  } else if (j0>51) {
51  if(j0==0x400) return x+x; /* inf or NaN */
52  else return x; /* x is integral */
53  } else {
54  i = ((u_int32_t)(0xffffffff))>>(j0-20);
55  if((i1&i)==0) return x; /* x is integral */
56  if(huge+x>0.0) { /* raise inexact flag */
57  if(i0<0) {
58  if(j0==20) i0+=1;
59  else {
60  j = i1+(1<<(52-j0));
61  if(j<(u_int32_t)i1) i0 +=1 ; /* got a carry */
62  i1=j;
63  }
64  }
65  i1 &= (~i);
66  }
67  }
68  INSERT_WORDS(x,i0,i1);
69  return x;
70 }
71 libm_hidden_def(floor)