floatunditf.c revision 276851 
1/* This file is distributed under the University of Illinois Open Source
2 * License. See LICENSE.TXT for details.
3 */
4
5/* long double __floatunditf(unsigned long long x); */
6/* This file implements the PowerPC unsigned long long -> long double conversion */
7
8#include "DD.h"
9
10long double __floatunditf(uint64_t a) {
11
12	/* Begins with an exact copy of the code from __floatundidf */
13
14	static const double twop52 = 0x1.0p52;
15	static const double twop84 = 0x1.0p84;
16	static const double twop84_plus_twop52 = 0x1.00000001p84;
17
18	doublebits high = { .d = twop84 };
19	doublebits low  = { .d = twop52 };
20
21	high.x |= a >> 32;							/* 0x1.0p84 + high 32 bits of a */
22	low.x |= a & UINT64_C(0x00000000ffffffff);	/* 0x1.0p52 + low 32 bits of a */
23
24	const double high_addend = high.d - twop84_plus_twop52;
25
26	/* At this point, we have two double precision numbers
27	 * high_addend and low.d, and we wish to return their sum
28	 * as a canonicalized long double:
29	 */
30
31	/* This implementation sets the inexact flag spuriously. */
32	/* This could be avoided, but at some substantial cost. */
33
34	DD result;
35
36	result.s.hi = high_addend + low.d;
37	result.s.lo = (high_addend - result.s.hi) + low.d;
38
39	return result.ld;
40
41}
42