compiler-rt/lib/ppc/floatditf.c

// 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"
#include <stdint.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.hi = high_addend + low.d;
	result.lo = (high_addend - result.hi) + low.d;
	
	return result.ld;
	
}