1 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
2 // See https://llvm.org/LICENSE.txt for license information.
3 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
4 
5 // int64_t __fixunstfdi(long double x);
6 // This file implements the PowerPC 128-bit double-double -> int64_t conversion
7 
8 #include "../int_math.h"
9 #include "DD.h"
10 
__fixtfdi(long double input)11 uint64_t __fixtfdi(long double input) {
12   const DD x = {.ld = input};
13   const doublebits hibits = {.d = x.s.hi};
14 
15   const uint32_t absHighWord =
16       (uint32_t)(hibits.x >> 32) & UINT32_C(0x7fffffff);
17   const uint32_t absHighWordMinusOne = absHighWord - UINT32_C(0x3ff00000);
18 
19   // If (1.0 - tiny) <= input < 0x1.0p63:
20   if (UINT32_C(0x03f00000) > absHighWordMinusOne) {
21     // Do an unsigned conversion of the absolute value, then restore the sign.
22     const int unbiasedHeadExponent = absHighWordMinusOne >> 20;
23 
24     int64_t result = hibits.x & INT64_C(0x000fffffffffffff); // mantissa(hi)
25     result |= INT64_C(0x0010000000000000); // matissa(hi) with implicit bit
26     result <<= 10; // mantissa(hi) with one zero preceding bit.
27 
28     const int64_t hiNegationMask = ((int64_t)(hibits.x)) >> 63;
29 
30     // If the tail is non-zero, we need to patch in the tail bits.
31     if (0.0 != x.s.lo) {
32       const doublebits lobits = {.d = x.s.lo};
33       int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
34       tailMantissa |= INT64_C(0x0010000000000000);
35 
36       // At this point we have the mantissa of |tail|
37       // We need to negate it if head and tail have different signs.
38       const int64_t loNegationMask = ((int64_t)(lobits.x)) >> 63;
39       const int64_t negationMask = loNegationMask ^ hiNegationMask;
40       tailMantissa = (tailMantissa ^ negationMask) - negationMask;
41 
42       // Now we have the mantissa of tail as a signed 2s-complement integer
43 
44       const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
45 
46       // Shift the tail mantissa into the right position, accounting for the
47       // bias of 10 that we shifted the head mantissa by.
48       tailMantissa >>=
49           (unbiasedHeadExponent - (biasedTailExponent - (1023 - 10)));
50 
51       result += tailMantissa;
52     }
53 
54     result >>= (62 - unbiasedHeadExponent);
55 
56     // Restore the sign of the result and return
57     result = (result ^ hiNegationMask) - hiNegationMask;
58     return result;
59   }
60 
61   // Edge cases handled here:
62 
63   // |x| < 1, result is zero.
64   if (1.0 > crt_fabs(x.s.hi))
65     return INT64_C(0);
66 
67   // x very close to INT64_MIN, care must be taken to see which side we are on.
68   if (x.s.hi == -0x1.0p63) {
69 
70     int64_t result = INT64_MIN;
71 
72     if (0.0 < x.s.lo) {
73       // If the tail is positive, the correct result is something other than
74       // INT64_MIN. we'll need to figure out what it is.
75 
76       const doublebits lobits = {.d = x.s.lo};
77       int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
78       tailMantissa |= INT64_C(0x0010000000000000);
79 
80       // Now we negate the tailMantissa
81       tailMantissa = (tailMantissa ^ INT64_C(-1)) + INT64_C(1);
82 
83       // And shift it by the appropriate amount
84       const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
85       tailMantissa >>= 1075 - biasedTailExponent;
86 
87       result -= tailMantissa;
88     }
89 
90     return result;
91   }
92 
93   // Signed overflows, infinities, and NaNs
94   if (x.s.hi > 0.0)
95     return INT64_MAX;
96   else
97     return INT64_MIN;
98 }
99