musl/src/math/truncl.c

/* origin: FreeBSD /usr/src/lib/msun/src/s_truncl.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.
 * ====================================================
 */
/*
 * truncl(x)
 * Return x rounded toward 0 to integral value
 * Method:
 *      Bit twiddling.
 * Exception:
 *      Inexact flag raised if x not equal to truncl(x).
 */

#include "libm.h"

#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
long double truncl(long double x)
{
	return trunc(x);
}
#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
#ifdef LDBL_IMPLICIT_NBIT
#define MANH_SIZE       (LDBL_MANH_SIZE + 1)
#else
#define MANH_SIZE       LDBL_MANH_SIZE
#endif

static const long double huge = 1.0e300;
static const float zero[] = { 0.0, -0.0 };

long double truncl(long double x)
{
	union IEEEl2bits u = { .e = x };
	int e = u.bits.exp - LDBL_MAX_EXP + 1;

	if (e < MANH_SIZE - 1) {
		if (e < 0) {
			/* raise inexact if x != 0 */
			if (huge + x > 0.0)
				u.e = zero[u.bits.sign];
		} else {
			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
			if (((u.bits.manh & m) | u.bits.manl) == 0)
				return x;     /* x is integral */
			/* raise inexact */
			if (huge + x > 0.0) {
				u.bits.manh &= ~m;
				u.bits.manl = 0;
			}
		}
	} else if (e < LDBL_MANT_DIG - 1) {
		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
		if ((u.bits.manl & m) == 0)
			return x;     /* x is integral */
		/* raise inexact */
		if (huge + x > 0.0)
			u.bits.manl &= ~m;
	}
	return u.e;
}
#endif