From f607e3e970fe0dc0e71b04e4a65f50e90aac74df Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Sun, 3 Apr 2022 08:44:51 -0700
Subject: [PATCH] Add __float128 support

---
 include/fmt/format-inl.h | 14 +++++++-------
 include/fmt/format.h     | 29 ++++++++++++++++-------------
 test/format-test.cc      |  6 ++++++
 3 files changed, 29 insertions(+), 20 deletions(-)

diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 0febc002..99023abd 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -234,10 +234,10 @@ template <typename F> struct basic_fp {
     // The predecessor is closer if n is a normalized power of 2 (f == 0) other
     // than the smallest normalized number (biased_e > 1).
     auto is_predecessor_closer = f == 0 && biased_e > 1;
-    if (biased_e != 0)
-      f += static_cast<F>(implicit_bit);
-    else
+    if (biased_e == 0)
       biased_e = 1;  // Subnormals use biased exponent 1 (min exponent).
+    else if (has_implicit_bit<Float>())
+      f += static_cast<F>(implicit_bit);
     e = biased_e - exponent_bias<Float>() - num_float_significand_bits;
     if (!has_implicit_bit<Float>()) ++e;
     return is_predecessor_closer;
@@ -2049,9 +2049,9 @@ enum dragon {
 // Formats a floating-point number using a variation of the Fixed-Precision
 // Positive Floating-Point Printout ((FPP)^2) algorithm by Steele & White:
 // https://fmt.dev/papers/p372-steele.pdf.
-FMT_CONSTEXPR20 inline void format_dragon(fp value, unsigned flags,
-                                          int num_digits, buffer<char>& buf,
-                                          int& exp10) {
+FMT_CONSTEXPR20 inline void format_dragon(basic_fp<uint128_t> value,
+                                          unsigned flags, int num_digits,
+                                          buffer<char>& buf, int& exp10) {
   bigint numerator;    // 2 * R in (FPP)^2.
   bigint denominator;  // 2 * S in (FPP)^2.
   // lower and upper are differences between value and corresponding boundaries.
@@ -2255,7 +2255,7 @@ FMT_HEADER_ONLY_CONSTEXPR20 int format_float(Float value, int precision,
     }
   }
   if (use_dragon) {
-    auto f = fp();
+    auto f = basic_fp<uint128_t>();
     bool is_predecessor_closer = specs.binary32
                                      ? f.assign(static_cast<float>(value))
                                      : f.assign(converted_value);
diff --git a/include/fmt/format.h b/include/fmt/format.h
index 63eed8bb..dbf92f1a 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -336,24 +336,26 @@ class uint128_fallback {
     return static_cast<T>(lo_);
   }
 
-  friend auto operator==(const uint128_fallback& lhs,
-                         const uint128_fallback& rhs) -> bool {
+  friend constexpr auto operator==(const uint128_fallback& lhs,
+                                   const uint128_fallback& rhs) -> bool {
     return lhs.hi_ == rhs.hi_ && lhs.lo_ == rhs.lo_;
   }
-  friend auto operator!=(const uint128_fallback& lhs,
-                         const uint128_fallback& rhs) -> bool {
+  friend constexpr auto operator!=(const uint128_fallback& lhs,
+                                   const uint128_fallback& rhs) -> bool {
     return !(lhs == rhs);
   }
-  friend auto operator>(const uint128_fallback& lhs,
-                        const uint128_fallback& rhs) -> bool {
+  friend constexpr auto operator>(const uint128_fallback& lhs,
+                                  const uint128_fallback& rhs) -> bool {
     return lhs.hi_ != rhs.hi_ ? lhs.hi_ > rhs.hi_ : lhs.lo_ > rhs.lo_;
   }
-  friend auto operator|(const uint128_fallback& lhs,
-                        const uint128_fallback& rhs) -> uint128_fallback {
+  friend constexpr auto operator|(const uint128_fallback& lhs,
+                                  const uint128_fallback& rhs)
+      -> uint128_fallback {
     return {lhs.hi_ | rhs.hi_, lhs.lo_ | rhs.lo_};
   }
-  friend auto operator&(const uint128_fallback& lhs,
-                        const uint128_fallback& rhs) -> uint128_fallback {
+  friend constexpr auto operator&(const uint128_fallback& lhs,
+                                  const uint128_fallback& rhs)
+      -> uint128_fallback {
     return {lhs.hi_ & rhs.hi_, lhs.lo_ & rhs.lo_};
   }
   friend auto operator+(const uint128_fallback& lhs,
@@ -366,12 +368,13 @@ class uint128_fallback {
       -> uint128_fallback {
     FMT_ASSERT(lhs.hi_ == 0, "");
     uint64_t hi = (lhs.lo_ >> 32) * rhs;
-    return {hi >> 32, (hi << 32) + (lhs.lo_ & ~uint32_t()) * rhs};
+    uint64_t lo = (lhs.lo_ & ~uint32_t()) * rhs;
+    uint64_t new_lo = (hi << 32) + lo;
+    return {(hi >> 32) + (new_lo < lo ? 1 : 0), new_lo};
   }
   friend auto operator-(const uint128_fallback& lhs, uint64_t rhs)
       -> uint128_fallback {
-    FMT_ASSERT(lhs.lo_ >= rhs, "");
-    return {lhs.hi_, lhs.lo_ - rhs};
+    return {lhs.hi_ - (lhs.lo_ < rhs ? 1 : 0), lhs.lo_ - rhs};
   }
   FMT_CONSTEXPR auto operator>>(int shift) const -> uint128_fallback {
     if (shift == 64) return {0, hi_};
diff --git a/test/format-test.cc b/test/format-test.cc
index b5ecd03c..5acffab9 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -75,6 +75,12 @@ TEST(uint128_test, plus_assign) {
   EXPECT_EQ(n, uint128_fallback(1) << 64);
 }
 
+TEST(uint128_test, multiply) {
+  auto n = uint128_fallback(2251799813685247);
+  n = n * 3611864890;
+  EXPECT_EQ(static_cast<uint64_t>(n >> 64), 440901);
+}
+
 template <typename Float> void check_isfinite() {
   using fmt::detail::isfinite;
   EXPECT_TRUE(isfinite(Float(0.0)));