forked from OSchip/llvm-project
47 lines
2.0 KiB
C
47 lines
2.0 KiB
C
//===-- lib/builtins/ppc/floattitf.c - Convert int128->long double -*-C -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements converting a signed 128 bit integer to a 128bit IBM /
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// PowerPC long double (double-double) value.
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//
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//===----------------------------------------------------------------------===//
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#include <stdint.h>
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// Conversions from signed and unsigned 64-bit int to long double.
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long double __floatditf(int64_t);
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long double __floatunditf(uint64_t);
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// Convert a signed 128-bit integer to long double.
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// This uses the following property: Let hi and lo be 64-bits each,
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// and let signed_val_k() and unsigned_val_k() be the value of the
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// argument interpreted as a signed or unsigned k-bit integer. Then,
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//
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// signed_val_128(hi,lo) = signed_val_64(hi) * 2^64 + unsigned_val_64(lo)
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// = (long double)hi * 2^64 + (long double)lo,
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//
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// where (long double)hi and (long double)lo are signed and
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// unsigned 64-bit integer to long double conversions, respectively.
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long double __floattitf(__int128_t arg) {
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// Split the int128 argument into 64-bit high and low int64 parts.
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int64_t ArgHiPart = (int64_t)(arg >> 64);
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uint64_t ArgLoPart = (uint64_t)arg;
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// Convert each 64-bit part into long double. The high part
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// must be a signed conversion and the low part an unsigned conversion
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// to ensure the correct result.
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long double ConvertedHiPart = __floatditf(ArgHiPart);
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long double ConvertedLoPart = __floatunditf(ArgLoPart);
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// The low bit of ArgHiPart corresponds to the 2^64 bit in arg.
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// Multiply the high part by 2^64 to undo the right shift by 64-bits
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// done in the splitting. Then, add to the low part to obtain the
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// final result.
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return ((ConvertedHiPart * 0x1.0p64) + ConvertedLoPart);
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}
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