58 lines
1.9 KiB
C
58 lines
1.9 KiB
C
// 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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// uint64_t __fixunstfdi(long double x);
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// This file implements the PowerPC 128-bit double-double -> uint64_t conversion
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#include "DD.h"
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uint64_t __fixunstfdi(long double input) {
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const DD x = {.ld = input};
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const doublebits hibits = {.d = x.s.hi};
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const uint32_t highWordMinusOne =
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(uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000);
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// If (1.0 - tiny) <= input < 0x1.0p64:
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if (UINT32_C(0x04000000) > highWordMinusOne) {
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const int unbiasedHeadExponent = highWordMinusOne >> 20;
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uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); // mantissa(hi)
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result |= UINT64_C(0x0010000000000000); // matissa(hi) with implicit bit
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result <<= 11; // mantissa(hi) left aligned in the int64 field.
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// If the tail is non-zero, we need to patch in the tail bits.
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if (0.0 != x.s.lo) {
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const doublebits lobits = {.d = x.s.lo};
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int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff);
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tailMantissa |= INT64_C(0x0010000000000000);
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// At this point we have the mantissa of |tail|
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const int64_t negationMask = ((int64_t)(lobits.x)) >> 63;
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tailMantissa = (tailMantissa ^ negationMask) - negationMask;
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// Now we have the mantissa of tail as a signed 2s-complement integer
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const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff;
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// Shift the tail mantissa into the right position, accounting for the
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// bias of 11 that we shifted the head mantissa by.
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tailMantissa >>=
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(unbiasedHeadExponent - (biasedTailExponent - (1023 - 11)));
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result += tailMantissa;
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}
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result >>= (63 - unbiasedHeadExponent);
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return result;
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}
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// Edge cases are handled here, with saturation.
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if (1.0 > x.s.hi)
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return UINT64_C(0);
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else
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return UINT64_MAX;
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}
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