fixunstfdi.c revision 2d1fdb26e458c4ddc04155c1d421bced3ba90cd0 
1/* This file is distributed under the University of Illinois Open Source
2 * License. See LICENSE.TXT for details.
3 */
4
5/* uint64_t __fixunstfdi(long double x); */
6/* This file implements the PowerPC 128-bit double-double -> uint64_t conversion */
7
8#include "DD.h"
9
10uint64_t __fixunstfdi(long double input)
11{
12	const DD x = { .ld = input };
13	const doublebits hibits = { .d = x.s.hi };
14
15	const uint32_t highWordMinusOne = (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000);
16
17	/* If (1.0 - tiny) <= input < 0x1.0p64: */
18	if (UINT32_C(0x04000000) > highWordMinusOne)
19	{
20		const int unbiasedHeadExponent = highWordMinusOne >> 20;
21
22		uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); /* mantissa(hi) */
23		result |= UINT64_C(0x0010000000000000); /* matissa(hi) with implicit bit */
24		result <<= 11; /* mantissa(hi) left aligned in the int64 field. */
25
26		/* If the tail is non-zero, we need to patch in the tail bits. */
27		if (0.0 != x.s.lo)
28		{
29			const doublebits lobits = { .d = x.s.lo };
30			int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
31			tailMantissa |= INT64_C(0x0010000000000000);
32
33			/* At this point we have the mantissa of |tail| */
34
35			const int64_t negationMask = ((int64_t)(lobits.x)) >> 63;
36			tailMantissa = (tailMantissa ^ negationMask) - negationMask;
37
38			/* Now we have the mantissa of tail as a signed 2s-complement integer */
39
40			const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
41
42			/* Shift the tail mantissa into the right position, accounting for the
43			 * bias of 11 that we shifted the head mantissa by.
44			 */
45			tailMantissa >>= (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11)));
46
47			result += tailMantissa;
48		}
49
50		result >>= (63 - unbiasedHeadExponent);
51		return result;
52	}
53
54	/* Edge cases are handled here, with saturation. */
55	if (1.0 > x.s.hi)
56		return UINT64_C(0);
57	else
58		return UINT64_MAX;
59}
60