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 
__floatunditf(uint64_t a)10 long 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