From a5aa5e2b2d75ffdee2d3bee24baab2b4befbe4de Mon Sep 17 00:00:00 2001
From: Yuri Kunde Schlesner <yuriks@yuriks.net>
Date: Sat, 9 Dec 2017 20:16:07 -0800
Subject: [PATCH] Common: Simplify and optimize BitSet iterator

Instead of doing complex machinations to keep track of the current bit
index, just unset the lowest bit on each iteration, greatly simplifying
the code.
---
 src/common/bit_set.h | 27 ++++++---------------------
 1 file changed, 6 insertions(+), 21 deletions(-)

diff --git a/src/common/bit_set.h b/src/common/bit_set.h
index 9c2e6b28c0..749de4df01 100644
--- a/src/common/bit_set.h
+++ b/src/common/bit_set.h
@@ -120,20 +120,15 @@ public:
     // A STL-like iterator is required to be able to use range-based for loops.
     class Iterator {
     public:
-        Iterator(const Iterator& other) : m_val(other.m_val), m_bit(other.m_bit) {}
-        Iterator(IntTy val) : m_val(val), m_bit(0) {}
-        Iterator& operator=(Iterator other) {
-            new (this) Iterator(other);
-            return *this;
-        }
+        Iterator(const Iterator& other) : m_val(other.m_val) {}
+        Iterator(IntTy val) : m_val(val) {}
         int operator*() {
-            return m_bit + ComputeLsb();
+            // This will never be called when m_val == 0, because that would be the end() iterator
+            return LeastSignificantSetBit(m_val);
         }
         Iterator& operator++() {
-            int lsb = ComputeLsb();
-            m_val >>= lsb + 1;
-            m_bit += lsb + 1;
-            m_has_lsb = false;
+            // Unset least significant set bit
+            m_val &= m_val - IntTy(1);
             return *this;
         }
         Iterator operator++(int _) {
@@ -149,17 +144,7 @@ public:
         }
 
     private:
-        int ComputeLsb() {
-            if (!m_has_lsb) {
-                m_lsb = LeastSignificantSetBit(m_val);
-                m_has_lsb = true;
-            }
-            return m_lsb;
-        }
         IntTy m_val;
-        int m_bit;
-        int m_lsb = -1;
-        bool m_has_lsb = false;
     };
 
     BitSet() : m_val(0) {}