compiler-rt/lib/builtins/ppc/floattitf.c

   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.
  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 }