floatditf.c   [plain text]

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

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

#include "DD.h"

long double __floatditf(int64_t a) {
	
	static const double twop32 = 0x1.0p32;
	static const double twop52 = 0x1.0p52;
	
	doublebits low  = { .d = twop52 };
	low.x |= a & UINT64_C(0x00000000ffffffff);	/* 0x1.0p52 + low 32 bits of a. */
	
	const double high_addend = (double)((int32_t)(a >> 32))*twop32 - 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;
	
}