diff options
Diffstat (limited to 'absl/numeric/int128_no_intrinsic.inc')
| -rw-r--r-- | absl/numeric/int128_no_intrinsic.inc | 77 |
1 files changed, 47 insertions, 30 deletions
diff --git a/absl/numeric/int128_no_intrinsic.inc b/absl/numeric/int128_no_intrinsic.inc index 8834804c..6f5d8377 100644 --- a/absl/numeric/int128_no_intrinsic.inc +++ b/absl/numeric/int128_no_intrinsic.inc @@ -23,8 +23,7 @@ constexpr int64_t Int128High64(int128 v) { return v.hi_; } #if defined(ABSL_IS_LITTLE_ENDIAN) -constexpr int128::int128(int64_t high, uint64_t low) : - lo_(low), hi_(high) {} +constexpr int128::int128(int64_t high, uint64_t low) : lo_(low), hi_(high) {} constexpr int128::int128(int v) : lo_{static_cast<uint64_t>(v)}, hi_{v < 0 ? ~int64_t{0} : 0} {} @@ -44,8 +43,7 @@ constexpr int128::int128(uint128 v) #elif defined(ABSL_IS_BIG_ENDIAN) -constexpr int128::int128(int64_t high, uint64_t low) : - hi_{high}, lo_{low} {} +constexpr int128::int128(int64_t high, uint64_t low) : hi_{high}, lo_{low} {} constexpr int128::int128(int v) : hi_{v < 0 ? ~int64_t{0} : 0}, lo_{static_cast<uint64_t>(v)} {} @@ -279,33 +277,52 @@ constexpr int128 operator^(int128 lhs, int128 rhs) { } constexpr int128 operator<<(int128 lhs, int amount) { - // int64_t shifts of >= 64 are undefined, so we need some special-casing. - return amount >= 64 - ? MakeInt128( - static_cast<int64_t>(Int128Low64(lhs) << (amount - 64)), 0) - : amount == 0 - ? lhs - : MakeInt128( - (Int128High64(lhs) << amount) | - static_cast<int64_t>(Int128Low64(lhs) >> (64 - amount)), - Int128Low64(lhs) << amount); + // int64_t shifts of >= 63 are undefined, so we need some special-casing. + assert(amount >= 0 && amount < 127); + if (amount <= 0) { + return lhs; + } else if (amount < 63) { + return MakeInt128( + (Int128High64(lhs) << amount) | + static_cast<int64_t>(Int128Low64(lhs) >> (64 - amount)), + Int128Low64(lhs) << amount); + } else if (amount == 63) { + return MakeInt128(((Int128High64(lhs) << 32) << 31) | + static_cast<int64_t>(Int128Low64(lhs) >> 1), + (Int128Low64(lhs) << 32) << 31); + } else if (amount == 127) { + return MakeInt128(static_cast<int64_t>(Int128Low64(lhs) << 63), 0); + } else if (amount > 127) { + return MakeInt128(0, 0); + } else { + // amount >= 64 && amount < 127 + return MakeInt128(static_cast<int64_t>(Int128Low64(lhs) << (amount - 64)), + 0); + } } constexpr int128 operator>>(int128 lhs, int amount) { - // int64_t shifts of >= 64 are undefined, so we need some special-casing. - // The (Int128High64(lhs) >> 32) >> 32 "trick" causes the the most significant - // int64 to be inititialized with all zeros or all ones correctly. It takes - // into account whether the number is negative or positive, and whether the - // current architecture does arithmetic or logical right shifts for negative - // numbers. - return amount >= 64 - ? MakeInt128( - (Int128High64(lhs) >> 32) >> 32, - static_cast<uint64_t>(Int128High64(lhs) >> (amount - 64))) - : amount == 0 - ? lhs - : MakeInt128(Int128High64(lhs) >> amount, - (Int128Low64(lhs) >> amount) | - (static_cast<uint64_t>(Int128High64(lhs)) - << (64 - amount))); + // int64_t shifts of >= 63 are undefined, so we need some special-casing. + assert(amount >= 0 && amount < 127); + if (amount <= 0) { + return lhs; + } else if (amount < 63) { + return MakeInt128( + Int128High64(lhs) >> amount, + Int128Low64(lhs) >> amount | static_cast<uint64_t>(Int128High64(lhs)) + << (64 - amount)); + } else if (amount == 63) { + return MakeInt128((Int128High64(lhs) >> 32) >> 31, + static_cast<uint64_t>(Int128High64(lhs) << 1) | + (Int128Low64(lhs) >> 32) >> 31); + + } else if (amount >= 127) { + return MakeInt128((Int128High64(lhs) >> 32) >> 31, + static_cast<uint64_t>((Int128High64(lhs) >> 32) >> 31)); + } else { + // amount >= 64 && amount < 127 + return MakeInt128( + (Int128High64(lhs) >> 32) >> 31, + static_cast<uint64_t>(Int128High64(lhs) >> (amount - 64))); + } } |