From a7fe7eb75957872935b934633ca3e614ed0944c5 Mon Sep 17 00:00:00 2001
From: Dominik Laskowski <domlaskowski@google.com>
Date: Wed, 16 Feb 2022 10:44:28 -0800
Subject: FTL: Remove libutils dependency of Flags

Also, fix the __builtin type suffix in flag_string to avoid truncation
of upper bits for 64-bit flags on platforms with 32-bit unsigned long.

Bug: 185536303
Test: ftl_test
Change-Id: I1719255cc4dd60ec3203e111c37d6851471c631d
---
 include/ftl/Flags.h    | 26 +++++++++++++-------------
 include/ftl/enum.h     |  4 ++--
 libs/ftl/Android.bp    |  8 --------
 libs/ftl/enum_test.cpp | 10 ++++++++++
 4 files changed, 25 insertions(+), 23 deletions(-)

diff --git a/include/ftl/Flags.h b/include/ftl/Flags.h
index 708eaf5dde..db3d9ea5b9 100644
--- a/include/ftl/Flags.h
+++ b/include/ftl/Flags.h
@@ -19,13 +19,12 @@
 #include <ftl/enum.h>
 #include <ftl/string.h>
 
+#include <bitset>
 #include <cstdint>
 #include <iterator>
 #include <string>
 #include <type_traits>
 
-#include "utils/BitSet.h"
-
 // TODO(b/185536303): Align with FTL style and namespace.
 
 namespace android {
@@ -56,21 +55,22 @@ public:
           : mFlags(t) {}
 
     class Iterator {
-        // The type can't be larger than 64-bits otherwise it won't fit in BitSet64.
-        static_assert(sizeof(U) <= sizeof(uint64_t));
+        using Bits = std::uint64_t;
+        static_assert(sizeof(U) <= sizeof(Bits));
 
     public:
+        constexpr Iterator() = default;
         Iterator(Flags<F> flags) : mRemainingFlags(flags.mFlags) { (*this)++; }
-        Iterator() : mRemainingFlags(0), mCurrFlag(static_cast<F>(0)) {}
 
         // Pre-fix ++
         Iterator& operator++() {
-            if (mRemainingFlags.isEmpty()) {
-                mCurrFlag = static_cast<F>(0);
+            if (mRemainingFlags.none()) {
+                mCurrFlag = 0;
             } else {
-                uint64_t bit = mRemainingFlags.clearLastMarkedBit(); // counts from left
-                const U flag = 1 << (64 - bit - 1);
-                mCurrFlag = static_cast<F>(flag);
+                // TODO: Replace with std::countr_zero in C++20.
+                const Bits bit = static_cast<Bits>(__builtin_ctzll(mRemainingFlags.to_ullong()));
+                mRemainingFlags.reset(static_cast<std::size_t>(bit));
+                mCurrFlag = static_cast<U>(static_cast<Bits>(1) << bit);
             }
             return *this;
         }
@@ -88,7 +88,7 @@ public:
 
         bool operator!=(Iterator other) const { return !(*this == other); }
 
-        F operator*() { return mCurrFlag; }
+        F operator*() const { return F{mCurrFlag}; }
 
         // iterator traits
 
@@ -107,8 +107,8 @@ public:
         using pointer = void;
 
     private:
-        BitSet64 mRemainingFlags;
-        F mCurrFlag;
+        std::bitset<sizeof(Bits) * 8> mRemainingFlags;
+        U mCurrFlag = 0;
     };
 
     /*
diff --git a/include/ftl/enum.h b/include/ftl/enum.h
index 5234c051b1..82af1d6cf8 100644
--- a/include/ftl/enum.h
+++ b/include/ftl/enum.h
@@ -261,10 +261,10 @@ constexpr std::optional<std::string_view> flag_name(E v) {
   const auto value = to_underlying(v);
 
   // TODO: Replace with std::popcount and std::countr_zero in C++20.
-  if (__builtin_popcountl(value) != 1) return {};
+  if (__builtin_popcountll(value) != 1) return {};
 
   constexpr auto kRange = details::EnumRange<E, details::FlagName>{};
-  return kRange.values[__builtin_ctzl(value)];
+  return kRange.values[__builtin_ctzll(value)];
 }
 
 // Returns a stringified enumerator, or its integral value if not named.
diff --git a/libs/ftl/Android.bp b/libs/ftl/Android.bp
index bc2eb23677..7175f0705b 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -30,12 +30,4 @@ cc_test {
         "-Wextra",
         "-Wpedantic",
     ],
-
-    header_libs: [
-        "libbase_headers",
-    ],
-
-    shared_libs: [
-        "libbase",
-    ],
 }
diff --git a/libs/ftl/enum_test.cpp b/libs/ftl/enum_test.cpp
index d8ce7a5e7b..5592a01fde 100644
--- a/libs/ftl/enum_test.cpp
+++ b/libs/ftl/enum_test.cpp
@@ -143,6 +143,16 @@ TEST(Enum, String) {
     EXPECT_EQ(ftl::flag_string(Flags::kNone), "0b0");
     EXPECT_EQ(ftl::flag_string(Flags::kMask), "0b10010010");
     EXPECT_EQ(ftl::flag_string(Flags::kAll), "0b11111111");
+
+    enum class Flags64 : std::uint64_t {
+      kFlag0 = 0b1ull,
+      kFlag63 = 0x8000'0000'0000'0000ull,
+      kMask = kFlag0 | kFlag63
+    };
+
+    EXPECT_EQ(ftl::flag_string(Flags64::kFlag0), "kFlag0");
+    EXPECT_EQ(ftl::flag_string(Flags64::kFlag63), "kFlag63");
+    EXPECT_EQ(ftl::flag_string(Flags64::kMask), "0x8000000000000001");
   }
   {
     EXPECT_EQ(ftl::enum_string(Planet::kEarth), "kEarth");
-- 
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