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 9c2e6b28c..749de4df0 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) {}