1 //===-- lib/builtins/ppc/floattitf.c - Convert int128->long double -*-C -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements converting a signed 128 bit integer to a 128bit IBM /
10 // PowerPC long double (double-double) value.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include <stdint.h>
15
16 // Conversions from signed and unsigned 64-bit int to long double.
17 long double __floatditf(int64_t);
18 long double __floatunditf(uint64_t);
19
20 // Convert a signed 128-bit integer to long double.
21 // This uses the following property: Let hi and lo be 64-bits each,
22 // and let signed_val_k() and unsigned_val_k() be the value of the
23 // argument interpreted as a signed or unsigned k-bit integer. Then,
24 //
25 // signed_val_128(hi,lo) = signed_val_64(hi) * 2^64 + unsigned_val_64(lo)
26 // = (long double)hi * 2^64 + (long double)lo,
27 //
28 // where (long double)hi and (long double)lo are signed and
29 // unsigned 64-bit integer to long double conversions, respectively.
__floattitf(__int128_t arg)30 long double __floattitf(__int128_t arg) {
31 // Split the int128 argument into 64-bit high and low int64 parts.
32 int64_t ArgHiPart = (int64_t)(arg >> 64);
33 uint64_t ArgLoPart = (uint64_t)arg;
34
35 // Convert each 64-bit part into long double. The high part
36 // must be a signed conversion and the low part an unsigned conversion
37 // to ensure the correct result.
38 long double ConvertedHiPart = __floatditf(ArgHiPart);
39 long double ConvertedLoPart = __floatunditf(ArgLoPart);
40
41 // The low bit of ArgHiPart corresponds to the 2^64 bit in arg.
42 // Multiply the high part by 2^64 to undo the right shift by 64-bits
43 // done in the splitting. Then, add to the low part to obtain the
44 // final result.
45 return ((ConvertedHiPart * 0x1.0p64) + ConvertedLoPart);
46 }
47