path: root/src/math/modf.c

/* origin: FreeBSD /usr/src/lib/msun/src/s_modf.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.
 * ====================================================
 */
/*
 * modf(double x, double *iptr)
 * return fraction part of x, and return x's integral part in *iptr.
 * Method:
 *      Bit twiddling.
 *
 * Exception:
 *      No exception.
 */

#include "libm.h"

static const double one = 1.0;

double modf(double x, double *iptr)
{
	int32_t i0,i1,j0;
	uint32_t i;

	EXTRACT_WORDS(i0, i1, x);
	j0 = ((i0>>20) & 0x7ff) - 0x3ff; /* exponent of x */
	if (j0 < 20) {  /* integer part in high x */
		if (j0 < 0) {  /* |x| < 1 */
			INSERT_WORDS(*iptr, i0 & 0x80000000, 0); /* *iptr = +-0 */
			return x;
		}
		i = 0x000fffff >> j0;
		if (((i0&i)|i1) == 0) {  /* x is integral */
			uint32_t high;
			*iptr = x;
			GET_HIGH_WORD(high, x);
			INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
			return x;
		}
		INSERT_WORDS(*iptr, i0&~i, 0);
		return x - *iptr;
	} else if (j0 > 51) {  /* no fraction part */
		uint32_t high;
		if (j0 == 0x400) {  /* inf/NaN */
			*iptr = x;
			return 0.0 / x;
		}
		*iptr = x*one;
		GET_HIGH_WORD(high, x);
		INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
		return x;
	} else {               /* fraction part in low x */
		i = (uint32_t)0xffffffff >> (j0 - 20);
		if ((i1&i) == 0) {  /* x is integral */
			uint32_t high;
			*iptr = x;
			GET_HIGH_WORD(high, x);
			INSERT_WORDS(x, high & 0x80000000, 0);  /* return +-0 */
			return x;
		}
		INSERT_WORDS(*iptr, i0, i1&~i);
		return x - *iptr;
	}
}