| 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 | // uint64_t __fixunstfdi(long double x); |
| 6 | // This file implements the PowerPC 128-bit double-double -> uint64_t conversion |
| 7 | |
| 8 | #include "DD.h" |
| 9 | |
| 10 | uint64_t __fixunstfdi(long double input) { |
| 11 | const DD x = {.ld = input}; |
| 12 | const doublebits hibits = {.d = x.s.hi}; |
| 13 | |
| 14 | const uint32_t highWordMinusOne = |
| 15 | (uint32_t)(hibits.x >> 32) - UINT32_C(0x3ff00000); |
| 16 | |
| 17 | // If (1.0 - tiny) <= input < 0x1.0p64: |
| 18 | if (UINT32_C(0x04000000) > highWordMinusOne) { |
| 19 | const int unbiasedHeadExponent = highWordMinusOne >> 20; |
| 20 | |
| 21 | uint64_t result = hibits.x & UINT64_C(0x000fffffffffffff); // mantissa(hi) |
| 22 | result |= UINT64_C(0x0010000000000000); // matissa(hi) with implicit bit |
| 23 | result <<= 11; // mantissa(hi) left aligned in the int64 field. |
| 24 | |
| 25 | // If the tail is non-zero, we need to patch in the tail bits. |
| 26 | if (0.0 != x.s.lo) { |
| 27 | const doublebits lobits = {.d = x.s.lo}; |
| 28 | int64_t tailMantissa = lobits.x & INT64_C(0x000fffffffffffff); |
| 29 | tailMantissa |= INT64_C(0x0010000000000000); |
| 30 | |
| 31 | // At this point we have the mantissa of |tail| |
| 32 | |
| 33 | const int64_t negationMask = ((int64_t)(lobits.x)) >> 63; |
| 34 | tailMantissa = (tailMantissa ^ negationMask) - negationMask; |
| 35 | |
| 36 | // Now we have the mantissa of tail as a signed 2s-complement integer |
| 37 | |
| 38 | const int biasedTailExponent = (int)(lobits.x >> 52) & 0x7ff; |
| 39 | |
| 40 | // Shift the tail mantissa into the right position, accounting for the |
| 41 | // bias of 11 that we shifted the head mantissa by. |
| 42 | tailMantissa >>= |
| 43 | (unbiasedHeadExponent - (biasedTailExponent - (1023 - 11))); |
| 44 | |
| 45 | result += tailMantissa; |
| 46 | } |
| 47 | |
| 48 | result >>= (63 - unbiasedHeadExponent); |
| 49 | return result; |
| 50 | } |
| 51 | |
| 52 | // Edge cases are handled here, with saturation. |
| 53 | if (1.0 > x.s.hi) |
| 54 | return UINT64_C(0); |
| 55 | else |
| 56 | return UINT64_MAX; |
| 57 | } |
| 58 |