Make mt-constants private to FX_Random.

Avoid a copy of a std::array<> in the process by inlining init in
the constructor itself.

Change-Id: I561ffc3a66ace36f0a839bd7c8830add2dc75739
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/149270
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

core/fxcrt/fx_random.cpp

diff --git a/core/fxcrt/fx_random.cpp b/core/fxcrt/fx_random.cpp
index cc3ef27..6e9db07 100644
--- a/core/fxcrt/fx_random.cpp
+++ b/core/fxcrt/fx_random.cpp
@@ -74,20 +74,15 @@
   return ++global_seed;
 }
 
-std::array<uint32_t, FX_Random::kStateSize> InitState(uint32_t seed) {
-  std::array<uint32_t, FX_Random::kStateSize> state;
-  state[0] = seed;
-  for (uint32_t i = 1; i < FX_Random::kStateSize; i++) {
-    const uint32_t prev = state[i - 1];
-    state[i] = (1812433253UL * (prev ^ (prev >> 30)) + i);
-  }
-  return state;
-}
-
 }  // namespace
 
-FX_Random::FX_Random(uint32_t seed)
-    : next_index_(kStateSize), state_(InitState(seed)) {}
+FX_Random::FX_Random(uint32_t seed) {
+  state_[0] = seed;
+  for (uint32_t i = 1; i < kStateSize; i++) {
+    const uint32_t prev = state_[i - 1];
+    state_[i] = (1812433253UL * (prev ^ (prev >> 30)) + i);
+  }
+}
 
 FX_Random::~FX_Random() = default;
 

core/fxcrt/fx_random.h

diff --git a/core/fxcrt/fx_random.h b/core/fxcrt/fx_random.h
index 0625f17..ed0da24 100644
--- a/core/fxcrt/fx_random.h
+++ b/core/fxcrt/fx_random.h
@@ -17,14 +17,14 @@
 // A Mersenne Twister (MT) pseudo-random number generator.
 class FX_Random {
  public:
-  static constexpr size_t kStateSize = 624;
-  static constexpr size_t kTwistOffset = 397;
-
   // Using a temporary MT generator, fills `buffer` with random 32-bit unsigned
   // integers.
   static void Fill(pdfium::span<uint32_t> buffer);
 
  private:
+  static constexpr size_t kStateSize = 624;
+  static constexpr size_t kTwistOffset = 397;
+
   explicit FX_Random(uint32_t seed);
 
   FX_Random(const FX_Random&) = delete;
@@ -35,7 +35,7 @@
   // Returns a single random 32-bit unsigned integer.
   uint32_t Generate();
 
-  uint32_t next_index_;
+  uint32_t next_index_ = kStateSize;
   std::array<uint32_t, kStateSize> state_;
 };