# shithub: 9ferno

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```/* derived from /netlib/fdlibm */

/* @(#)s_floor.c 1.3 95/01/18 */
/*
* ====================================================
*
* Developed at SunSoft, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

/*
* floor(x)
* Return x rounded toward -inf to integral value
* Method:
*	Bit twiddling.
* Exception:
*	Inexact flag raised if x not equal to floor(x).
*/

#include "fdlibm.h"

static const double Huge = 1.0e300;

double floor(double x)
{
int i0,i1,j0;
unsigned i,j;
i0 =  __HI(x);
i1 =  __LO(x);
j0 = ((i0>>20)&0x7ff)-0x3ff;
if(j0<20) {
if(j0<0) { 	/* raise inexact if x != 0 */
if(Huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
if(i0>=0) {i0=i1=0;}
else if(((i0&0x7fffffff)|i1)!=0)
{ i0=0xbff00000;i1=0;}
}
} else {
i = (0x000fffff)>>j0;
if(((i0&i)|i1)==0) return x; /* x is integral */
if(Huge+x>0.0) {	/* raise inexact flag */
if(i0<0) i0 += (0x00100000)>>j0;
i0 &= (~i); i1=0;
}
}
} else if (j0>51) {
if(j0==0x400) return x+x;	/* inf or NaN */
else return x;		/* x is integral */
} else {
i = ((unsigned)(0xffffffff))>>(j0-20);
if((i1&i)==0) return x;	/* x is integral */
if(Huge+x>0.0) { 		/* raise inexact flag */
if(i0<0) {
if(j0==20) i0+=1;
else {
j = i1+(1<<(52-j0));
if(j<i1) i0 +=1 ; 	/* got a carry */
i1=j;
}
}
i1 &= (~i);
}
}
__HI(x) = i0;
__LO(x) = i1;
return x;
}
```