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-rw-r--r--absl/numeric/int128.h99
1 files changed, 42 insertions, 57 deletions
diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index d87cbbd4..5e1b3f03 100644
--- a/absl/numeric/int128.h
+++ b/absl/numeric/int128.h
@@ -62,7 +62,7 @@ namespace absl {
// However, a `uint128` differs from intrinsic integral types in the following
// ways:
//
-// * Errors on implicit conversions that does not preserve value (such as
+// * Errors on implicit conversions that do not preserve value (such as
// loss of precision when converting to float values).
// * Requires explicit construction from and conversion to floating point
// types.
@@ -71,8 +71,8 @@ namespace absl {
//
// Example:
//
-// float y = absl::kuint128max; // Error. uint128 cannot be implicitly
-// // converted to float.
+// float y = absl::Uint128Max(); // Error. uint128 cannot be implicitly
+// // converted to float.
//
// absl::uint128 v;
// absl::uint64_t i = v; // Error
@@ -175,10 +175,15 @@ class alignas(16) uint128 {
// Example:
//
// absl::uint128 big = absl::MakeUint128(1, 0);
- friend constexpr uint128 MakeUint128(uint64_t top, uint64_t bottom);
+ friend constexpr uint128 MakeUint128(uint64_t high, uint64_t low);
+
+ // Uint128Max()
+ //
+ // Returns the highest value for a 128-bit unsigned integer.
+ friend constexpr uint128 Uint128Max();
private:
- constexpr uint128(uint64_t top, uint64_t bottom);
+ constexpr uint128(uint64_t high, uint64_t low);
// TODO(strel) Update implementation to use __int128 once all users of
// uint128 are fixed to not depend on alignof(uint128) == 8. Also add
@@ -195,10 +200,13 @@ class alignas(16) uint128 {
#endif // byte order
};
+// Prefer to use the constexpr `Uint128Max()`.
+//
+// TODO(absl-team) deprecate kuint128max once migration tool is released.
extern const uint128 kuint128max;
// allow uint128 to be logged
-extern std::ostream& operator<<(std::ostream& o, uint128 b);
+extern std::ostream& operator<<(std::ostream& os, uint128 v);
// TODO(strel) add operator>>(std::istream&, uint128)
@@ -208,8 +216,13 @@ extern std::ostream& operator<<(std::ostream& o, uint128 b);
// Implementation details follow
// --------------------------------------------------------------------------
-constexpr uint128 MakeUint128(uint64_t top, uint64_t bottom) {
- return uint128(top, bottom);
+constexpr uint128 MakeUint128(uint64_t high, uint64_t low) {
+ return uint128(high, low);
+}
+
+constexpr uint128 Uint128Max() {
+ return uint128(std::numeric_limits<uint64_t>::max(),
+ std::numeric_limits<uint64_t>::max());
}
// Assignment from integer types.
@@ -251,33 +264,19 @@ inline uint128& uint128::operator=(unsigned __int128 v) {
// Shift and arithmetic operators.
-inline uint128 operator<<(uint128 lhs, int amount) {
- return uint128(lhs) <<= amount;
-}
+inline uint128 operator<<(uint128 lhs, int amount) { return lhs <<= amount; }
-inline uint128 operator>>(uint128 lhs, int amount) {
- return uint128(lhs) >>= amount;
-}
+inline uint128 operator>>(uint128 lhs, int amount) { return lhs >>= amount; }
-inline uint128 operator+(uint128 lhs, uint128 rhs) {
- return uint128(lhs) += rhs;
-}
+inline uint128 operator+(uint128 lhs, uint128 rhs) { return lhs += rhs; }
-inline uint128 operator-(uint128 lhs, uint128 rhs) {
- return uint128(lhs) -= rhs;
-}
+inline uint128 operator-(uint128 lhs, uint128 rhs) { return lhs -= rhs; }
-inline uint128 operator*(uint128 lhs, uint128 rhs) {
- return uint128(lhs) *= rhs;
-}
+inline uint128 operator*(uint128 lhs, uint128 rhs) { return lhs *= rhs; }
-inline uint128 operator/(uint128 lhs, uint128 rhs) {
- return uint128(lhs) /= rhs;
-}
+inline uint128 operator/(uint128 lhs, uint128 rhs) { return lhs /= rhs; }
-inline uint128 operator%(uint128 lhs, uint128 rhs) {
- return uint128(lhs) %= rhs;
-}
+inline uint128 operator%(uint128 lhs, uint128 rhs) { return lhs %= rhs; }
constexpr uint64_t Uint128Low64(uint128 v) { return v.lo_; }
@@ -287,8 +286,8 @@ constexpr uint64_t Uint128High64(uint128 v) { return v.hi_; }
#if defined(ABSL_IS_LITTLE_ENDIAN)
-constexpr uint128::uint128(uint64_t top, uint64_t bottom)
- : lo_(bottom), hi_(top) {}
+constexpr uint128::uint128(uint64_t high, uint64_t low)
+ : lo_(low), hi_(high) {}
constexpr uint128::uint128(int v)
: lo_(v), hi_(v < 0 ? std::numeric_limits<uint64_t>::max() : 0) {}
@@ -314,8 +313,8 @@ constexpr uint128::uint128(unsigned __int128 v)
#elif defined(ABSL_IS_BIG_ENDIAN)
-constexpr uint128::uint128(uint64_t top, uint64_t bottom)
- : hi_(top), lo_(bottom) {}
+constexpr uint128::uint128(uint64_t high, uint64_t low)
+ : hi_(high), lo_(low) {}
constexpr uint128::uint128(int v)
: hi_(v < 0 ? std::numeric_limits<uint64_t>::max() : 0), lo_(v) {}
@@ -460,13 +459,10 @@ inline bool operator>=(uint128 lhs, uint128 rhs) {
// Unary operators.
inline uint128 operator-(uint128 val) {
- const uint64_t hi_flip = ~Uint128High64(val);
- const uint64_t lo_flip = ~Uint128Low64(val);
- const uint64_t lo_add = lo_flip + 1;
- if (lo_add < lo_flip) {
- return MakeUint128(hi_flip + 1, lo_add);
- }
- return MakeUint128(hi_flip, lo_add);
+ uint64_t hi = ~Uint128High64(val);
+ uint64_t lo = ~Uint128Low64(val) + 1;
+ if (lo == 0) ++hi; // carry
+ return MakeUint128(hi, lo);
}
inline bool operator!(uint128 val) {
@@ -515,8 +511,8 @@ inline uint128& uint128::operator^=(uint128 other) {
// Shift and arithmetic assign operators.
inline uint128& uint128::operator<<=(int amount) {
- // Shifts of >= 128 are undefined.
- assert(amount < 128);
+ assert(amount >= 0); // Negative shifts are undefined.
+ assert(amount < 128); // Shifts of >= 128 are undefined.
// uint64_t shifts of >= 64 are undefined, so we will need some
// special-casing.
@@ -533,8 +529,8 @@ inline uint128& uint128::operator<<=(int amount) {
}
inline uint128& uint128::operator>>=(int amount) {
- // Shifts of >= 128 are undefined.
- assert(amount < 128);
+ assert(amount >= 0); // Negative shifts are undefined.
+ assert(amount < 128); // Shifts of >= 128 are undefined.
// uint64_t shifts of >= 64 are undefined, so we will need some
// special-casing.
@@ -574,25 +570,14 @@ inline uint128& uint128::operator*=(uint128 other) {
static_cast<unsigned __int128>(other);
return *this;
#else // ABSL_HAVE_INTRINSIC128
- uint64_t a96 = hi_ >> 32;
- uint64_t a64 = hi_ & 0xffffffff;
uint64_t a32 = lo_ >> 32;
uint64_t a00 = lo_ & 0xffffffff;
- uint64_t b96 = other.hi_ >> 32;
- uint64_t b64 = other.hi_ & 0xffffffff;
uint64_t b32 = other.lo_ >> 32;
uint64_t b00 = other.lo_ & 0xffffffff;
- // multiply [a96 .. a00] x [b96 .. b00]
- // terms higher than c96 disappear off the high side
- // terms c96 and c64 are safe to ignore carry bit
- uint64_t c96 = a96 * b00 + a64 * b32 + a32 * b64 + a00 * b96;
- uint64_t c64 = a64 * b00 + a32 * b32 + a00 * b64;
- this->hi_ = (c96 << 32) + c64;
- this->lo_ = 0;
- // add terms after this one at a time to capture carry
+ hi_ = hi_ * other.lo_ + lo_ * other.hi_ + a32 * b32;
+ lo_ = a00 * b00;
*this += uint128(a32 * b00) << 32;
*this += uint128(a00 * b32) << 32;
- *this += a00 * b00;
return *this;
#endif // ABSL_HAVE_INTRINSIC128
}
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