70 lines
1.7 KiB
C
70 lines
1.7 KiB
C
/*
|
|
* ====================================================
|
|
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
|
|
*
|
|
* Developed at SunPro, a Sun Microsystems, Inc. business.
|
|
* Permission to use, copy, modify, and distribute this
|
|
* software is freely granted, provided that this notice
|
|
* is preserved.
|
|
* ====================================================
|
|
*/
|
|
|
|
#include "fdlibm.h"
|
|
|
|
#ifndef _DOUBLE_IS_32BITS
|
|
|
|
#ifdef __STDC__
|
|
double trunc(double x)
|
|
#else
|
|
double trunc(x)
|
|
double x;
|
|
#endif
|
|
{
|
|
int signbit;
|
|
/* Most significant word, least significant word. */
|
|
int msw;
|
|
unsigned int lsw;
|
|
int exponent_less_1023;
|
|
|
|
EXTRACT_WORDS(msw, lsw, x);
|
|
|
|
/* Extract sign bit. */
|
|
signbit = msw & 0x80000000;
|
|
|
|
/* Extract exponent field. */
|
|
exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;
|
|
|
|
if (exponent_less_1023 < 20)
|
|
{
|
|
/* All significant digits are in msw. */
|
|
if (exponent_less_1023 < 0)
|
|
{
|
|
/* -1 < x < 1, so result is +0 or -0. */
|
|
INSERT_WORDS(x, signbit, 0);
|
|
}
|
|
else
|
|
{
|
|
/* All relevant fraction bits are in msw, so lsw of the result is 0. */
|
|
INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 0);
|
|
}
|
|
}
|
|
else if (exponent_less_1023 > 51)
|
|
{
|
|
if (exponent_less_1023 == 1024)
|
|
{
|
|
/* x is infinite, or not a number, so trigger an exception. */
|
|
return x + x;
|
|
}
|
|
/* All bits in the fraction fields of the msw and lsw are needed in the result. */
|
|
}
|
|
else
|
|
{
|
|
/* All fraction bits in msw are relevant. Truncate irrelevant
|
|
bits from lsw. */
|
|
INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20)));
|
|
}
|
|
return x;
|
|
}
|
|
|
|
#endif /* _DOUBLE_IS_32BITS */
|