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-rw-r--r--absl/numeric/int128.cc34
-rw-r--r--absl/numeric/int128.h99
-rw-r--r--absl/numeric/int128_have_intrinsic.inc19
-rw-r--r--absl/numeric/int128_no_intrinsic.inc19
-rw-r--r--absl/numeric/int128_test.cc6
5 files changed, 100 insertions, 77 deletions
diff --git a/absl/numeric/int128.cc b/absl/numeric/int128.cc
index 00bf7f47a4a2..de1b997ad159 100644
--- a/absl/numeric/int128.cc
+++ b/absl/numeric/int128.cc
@@ -139,9 +139,9 @@ uint128& uint128::operator%=(uint128 other) {
   return *this;
 }
 
-std::ostream& operator<<(std::ostream& o, uint128 b) {
-  std::ios_base::fmtflags flags = o.flags();
+namespace {
 
+std::string Uint128ToFormattedString(uint128 v, std::ios_base::fmtflags flags) {
   // Select a divisor which is the largest power of the base < 2^64.
   uint128 div;
   int div_base_log;
@@ -160,14 +160,14 @@ std::ostream& operator<<(std::ostream& o, uint128 b) {
       break;
   }
 
-  // Now piece together the uint128 representation from three chunks of
-  // the original value, each less than "div" and therefore representable
-  // as a uint64_t.
+  // Now piece together the uint128 representation from three chunks of the
+  // original value, each less than "div" and therefore representable as a
+  // uint64_t.
   std::ostringstream os;
   std::ios_base::fmtflags copy_mask =
       std::ios::basefield | std::ios::showbase | std::ios::uppercase;
   os.setf(flags & copy_mask, copy_mask);
-  uint128 high = b;
+  uint128 high = v;
   uint128 low;
   DivModImpl(high, div, &high, &low);
   uint128 mid;
@@ -182,25 +182,31 @@ std::ostream& operator<<(std::ostream& o, uint128 b) {
     os << std::noshowbase << std::setfill('0') << std::setw(div_base_log);
   }
   os << Uint128Low64(low);
-  std::string rep = os.str();
+  return os.str();
+}
+
+}  // namespace
+
+std::ostream& operator<<(std::ostream& os, uint128 v) {
+  std::ios_base::fmtflags flags = os.flags();
+  std::string rep = Uint128ToFormattedString(v, flags);
 
   // Add the requisite padding.
-  std::streamsize width = o.width(0);
+  std::streamsize width = os.width(0);
   if (static_cast<size_t>(width) > rep.size()) {
     std::ios::fmtflags adjustfield = flags & std::ios::adjustfield;
     if (adjustfield == std::ios::left) {
-      rep.append(width - rep.size(), o.fill());
+      rep.append(width - rep.size(), os.fill());
     } else if (adjustfield == std::ios::internal &&
                (flags & std::ios::showbase) &&
-               (flags & std::ios::basefield) == std::ios::hex && b != 0) {
-      rep.insert(2, width - rep.size(), o.fill());
+               (flags & std::ios::basefield) == std::ios::hex && v != 0) {
+      rep.insert(2, width - rep.size(), os.fill());
     } else {
-      rep.insert(0, width - rep.size(), o.fill());
+      rep.insert(0, width - rep.size(), os.fill());
     }
   }
 
-  // Stream the final representation in a single "<<" call.
-  return o << rep;
+  return os << rep;
 }
 
 }  // namespace absl
diff --git a/absl/numeric/int128.h b/absl/numeric/int128.h
index d87cbbd44752..5e1b3f03c0f2 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
 }
diff --git a/absl/numeric/int128_have_intrinsic.inc b/absl/numeric/int128_have_intrinsic.inc
index 49bde0767870..ee2a093018d9 100644
--- a/absl/numeric/int128_have_intrinsic.inc
+++ b/absl/numeric/int128_have_intrinsic.inc
@@ -1,3 +1,18 @@
-// This file will contain :int128 implementation details that depend on internal
-// representation when ABSL_HAVE_INTRINSIC_INT128 is defined. This file will be
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file contains :int128 implementation details that depend on internal
+// representation when ABSL_HAVE_INTRINSIC_INT128 is defined. This file is
 // included by int128.h.
diff --git a/absl/numeric/int128_no_intrinsic.inc b/absl/numeric/int128_no_intrinsic.inc
index 2dbff2b31565..0d0b3cfdeb12 100644
--- a/absl/numeric/int128_no_intrinsic.inc
+++ b/absl/numeric/int128_no_intrinsic.inc
@@ -1,3 +1,18 @@
-// This file will contain :int128 implementation details that depend on internal
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file contains :int128 implementation details that depend on internal
 // representation when ABSL_HAVE_INTRINSIC_INT128 is *not* defined. This file
-// will be included by int128.h.
+// is included by int128.h.
diff --git a/absl/numeric/int128_test.cc b/absl/numeric/int128_test.cc
index d674cb125f5e..79bcca907ae9 100644
--- a/absl/numeric/int128_test.cc
+++ b/absl/numeric/int128_test.cc
@@ -110,7 +110,7 @@ TEST(Uint128, AllTests) {
   absl::uint128 big = absl::MakeUint128(2000, 2);
   absl::uint128 big_minus_one = absl::MakeUint128(2000, 1);
   absl::uint128 bigger = absl::MakeUint128(2001, 1);
-  absl::uint128 biggest = absl::kuint128max;
+  absl::uint128 biggest = absl::Uint128Max();
   absl::uint128 high_low = absl::MakeUint128(1, 0);
   absl::uint128 low_high =
       absl::MakeUint128(0, std::numeric_limits<uint64_t>::max());
@@ -227,8 +227,10 @@ TEST(Uint128, AllTests) {
 
   EXPECT_EQ(big, -(-big));
   EXPECT_EQ(two, -((-one) - 1));
-  EXPECT_EQ(absl::kuint128max, -one);
+  EXPECT_EQ(absl::Uint128Max(), -one);
   EXPECT_EQ(zero, -zero);
+
+  EXPECT_EQ(absl::Uint128Max(), absl::kuint128max);
 }
 
 TEST(Uint128, ConversionTests) {
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