From 00dae56e1939ef14bb900cab9b472dfd001f8e37 Mon Sep 17 00:00:00 2001
From: Benny Halevy <bhalevy@scylladb.com>
Date: Sun, 29 May 2022 13:12:33 +0300
Subject: [PATCH] utils: dynamic_bitset: mark functions noexcept

dynamic_bitset allocates only when constructed.
then on it doesn't throw.

Though not that accessing bits out of range
is undefined behavior.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
---
 utils/dynamic_bitset.cc | 10 +++++-----
 utils/dynamic_bitset.hh | 25 ++++++++++++++-----------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/utils/dynamic_bitset.cc b/utils/dynamic_bitset.cc
index 160c060f93..6fb98fb38d 100644
--- a/utils/dynamic_bitset.cc
+++ b/utils/dynamic_bitset.cc
@@ -16,7 +16,7 @@
 
 namespace utils {
 
-void dynamic_bitset::set(size_t n) {
+void dynamic_bitset::set(size_t n) noexcept {
     for (auto& level : _bits) {
         auto idx = n / bits_per_int;
         auto old = level[idx];
@@ -28,7 +28,7 @@ void dynamic_bitset::set(size_t n) {
     }
 }
 
-void dynamic_bitset::clear(size_t n) {
+void dynamic_bitset::clear(size_t n) noexcept {
     for (auto& level : _bits) {
         auto idx = n / bits_per_int;
         auto old = level[idx];
@@ -40,7 +40,7 @@ void dynamic_bitset::clear(size_t n) {
     }
 }
 
-size_t dynamic_bitset::find_first_set() const
+size_t dynamic_bitset::find_first_set() const noexcept
 {
     size_t pos = 0;
     for (auto& vv : _bits | boost::adaptors::reversed) {
@@ -55,7 +55,7 @@ size_t dynamic_bitset::find_first_set() const
     return pos;
 }
 
-size_t dynamic_bitset::find_next_set(size_t n) const
+size_t dynamic_bitset::find_next_set(size_t n) const noexcept
 {
     ++n;
 
@@ -91,7 +91,7 @@ size_t dynamic_bitset::find_next_set(size_t n) const
     return n;
 }
 
-size_t dynamic_bitset::find_last_set() const
+size_t dynamic_bitset::find_last_set() const noexcept
 {
     size_t pos = 0;
     for (auto& vv : _bits | boost::adaptors::reversed) {
diff --git a/utils/dynamic_bitset.hh b/utils/dynamic_bitset.hh
index f0d0ab01fd..da8a280d26 100644
--- a/utils/dynamic_bitset.hh
+++ b/utils/dynamic_bitset.hh
@@ -26,19 +26,19 @@ private:
     size_t _bits_count = 0;
 private:
     // For n in range 0..(bits_per_int-1), produces a mask with all bits < n set
-    static int_type mask_lower_bits(size_t n) {
+    static int_type mask_lower_bits(size_t n) noexcept {
         return (int_type(1) << n) - 1;
     }
     // For n in range 0..(bits_per_int-1), produces a mask with all bits >= n set
-    static int_type mask_higher_bits(size_t n) {
+    static int_type mask_higher_bits(size_t n) noexcept {
         return ~mask_lower_bits(n);
     }
     // For bit n, produce index into _bits[level]
-    static size_t level_idx(unsigned level, size_t n) {
+    static size_t level_idx(unsigned level, size_t n) noexcept {
         return n >> ((level + 1) * level_shift);
     }
     // For bit n, produce bit number in _bits[level][level_idx]
-    static unsigned level_remainder(unsigned level, size_t n) {
+    static unsigned level_remainder(unsigned level, size_t n) noexcept {
         return (n >> (level * level_shift)) & (bits_per_int - 1);
     }
 public:
@@ -48,18 +48,21 @@ public:
 public:
     explicit dynamic_bitset(size_t nr_bits);
 
-    bool test(size_t n) const {
+    // undefined if n >= size
+    bool test(size_t n) const noexcept {
         auto idx = n / bits_per_int;
         return _bits[0][idx] & (int_type(1u) << (n % bits_per_int));
     }
-    void set(size_t n);
-    void clear(size_t n);
+    // undefined if n >= size
+    void set(size_t n) noexcept;
+    // undefined if n >= size
+    void clear(size_t n) noexcept;
 
-    size_t size() const { return _bits_count; }
+    size_t size() const noexcept { return _bits_count; }
 
-    size_t find_first_set() const;
-    size_t find_next_set(size_t n) const;
-    size_t find_last_set() const;
+    size_t find_first_set() const noexcept;
+    size_t find_next_set(size_t n) const noexcept;
+    size_t find_last_set() const noexcept;
 };
 
 }