xref: /aosp_15_r20/external/compiler-rt/lib/builtins/ppc/floatunditf.c (revision 7c3d14c8b49c529e04be81a3ce6f5cc23712e4c6)

/* This file is distributed under the University of Illinois Open Source
 * License. See LICENSE.TXT for details.
 */

/* long double __floatunditf(unsigned long long x); */
/* This file implements the PowerPC unsigned long long -> long double conversion */

#include "DD.h"

long double __floatunditf(uint64_t a) {

	/* Begins with an exact copy of the code from __floatundidf */

	static const double twop52 = 0x1.0p52;
	static const double twop84 = 0x1.0p84;
	static const double twop84_plus_twop52 = 0x1.00000001p84;

	doublebits high = { .d = twop84 };
	doublebits low  = { .d = twop52 };

	high.x |= a >> 32;							/* 0x1.0p84 + high 32 bits of a */
	low.x |= a & UINT64_C(0x00000000ffffffff);	/* 0x1.0p52 + low 32 bits of a */

	const double high_addend = high.d - twop84_plus_twop52;

	/* At this point, we have two double precision numbers
	 * high_addend and low.d, and we wish to return their sum
	 * as a canonicalized long double:
	 */

	/* This implementation sets the inexact flag spuriously. */
	/* This could be avoided, but at some substantial cost. */

	DD result;

	result.s.hi = high_addend + low.d;
	result.s.lo = (high_addend - result.s.hi) + low.d;

	return result.ld;

}