From 6849b541e9fd4b251e5a4bbaa241f68fb965588b Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Wed, 3 Sep 2025 22:28:18 -0700
Subject: [PATCH] [common] move bit-related macros to `bit_utils.hpp` (#11890)

This change moves the `kBitsPerByte` constant and the `BitSizeOf()`
and `BytesForBitSize()` macros from `numeric_limits.hpp` to the
more specialized `bit_utils.hpp` header.

This consolidation places common bit-utility definitions into a more
appropriate, dedicated header, improving code organization and
logical grouping. Headers that relied on these definitions are
updated accordingly.
---
 src/core/common/bit_set.hpp        |  2 +-
 src/core/common/bit_utils.hpp      | 20 ++++++++++++++++++++
 src/core/common/numeric_limits.hpp | 20 --------------------
 src/core/common/time_ticker.hpp    |  2 +-
 src/core/net/ip6_address.hpp       |  3 +--
 5 files changed, 23 insertions(+), 24 deletions(-)

diff --git a/src/core/common/bit_set.hpp b/src/core/common/bit_set.hpp
index 78dc4676f..c26777342 100644
--- a/src/core/common/bit_set.hpp
+++ b/src/core/common/bit_set.hpp
@@ -36,9 +36,9 @@
 
 #include "openthread-core-config.h"
 
+#include "common/bit_utils.hpp"
 #include "common/clearable.hpp"
 #include "common/equatable.hpp"
-#include "common/numeric_limits.hpp"
 
 namespace ot {
 
diff --git a/src/core/common/bit_utils.hpp b/src/core/common/bit_utils.hpp
index cc269c08e..8169b53d9 100644
--- a/src/core/common/bit_utils.hpp
+++ b/src/core/common/bit_utils.hpp
@@ -40,6 +40,26 @@
 
 namespace ot {
 
+static constexpr uint8_t kBitsPerByte = 8; ///< Number of bits in a byte.
+
+/**
+ * Returns the bit-size (number of bits) of a given type or variable.
+ *
+ * @param[in] aItem   The item (type or variable or expression) to get the bit-size of.
+ *
+ * @returns Number of bits of @p aItem.
+ */
+#define BitSizeOf(aItem) (sizeof(aItem) * kBitsPerByte)
+
+/**
+ * Determines number of bytes to represent a given number of bits.
+ *
+ * @param[in] aBitSize    The bit-size (number of bits).
+ *
+ * @returns Number of bytes to represent @p aBitSize.
+ */
+#define BytesForBitSize(aBitSize) static_cast<uint8_t>(((aBitSize) + (kBitsPerByte - 1)) / kBitsPerByte)
+
 /**
  * Counts the number of `1` bits in the binary representation of a given unsigned int bit-mask value.
  *
diff --git a/src/core/common/numeric_limits.hpp b/src/core/common/numeric_limits.hpp
index 122cdc35e..c104f5381 100644
--- a/src/core/common/numeric_limits.hpp
+++ b/src/core/common/numeric_limits.hpp
@@ -38,26 +38,6 @@
 
 namespace ot {
 
-static constexpr uint8_t kBitsPerByte = 8; ///< Number of bits in a byte.
-
-/**
- * Returns the bit-size (number of bits) of a given type or variable.
- *
- * @param[in] aItem   The item (type or variable or expression) to get the bit-size of.
- *
- * @returns Number of bits of @p aItem.
- */
-#define BitSizeOf(aItem) (sizeof(aItem) * kBitsPerByte)
-
-/**
- * Determines number of byes to represent a given number of bits.
- *
- * @param[in] aBitSize    The bit-size (number of bits).
- *
- * @returns Number of bytes to represent @p aBitSize.
- */
-#define BytesForBitSize(aBitSize) static_cast<uint8_t>(((aBitSize) + (kBitsPerByte - 1)) / kBitsPerByte)
-
 /**
  * Provides a way to query properties of arithmetic types.
  *
diff --git a/src/core/common/time_ticker.hpp b/src/core/common/time_ticker.hpp
index 55873a3b7..f05fde339 100644
--- a/src/core/common/time_ticker.hpp
+++ b/src/core/common/time_ticker.hpp
@@ -36,9 +36,9 @@
 
 #include "openthread-core-config.h"
 
+#include "common/bit_utils.hpp"
 #include "common/locator.hpp"
 #include "common/non_copyable.hpp"
-#include "common/numeric_limits.hpp"
 #include "common/time.hpp"
 #include "common/timer.hpp"
 
diff --git a/src/core/net/ip6_address.hpp b/src/core/net/ip6_address.hpp
index 16b197ce2..aeb0e11f0 100644
--- a/src/core/net/ip6_address.hpp
+++ b/src/core/net/ip6_address.hpp
@@ -39,11 +39,10 @@
 #include <openthread/ip6.h>
 
 #include "common/as_core_type.hpp"
+#include "common/bit_utils.hpp"
 #include "common/clearable.hpp"
 #include "common/encoding.hpp"
 #include "common/equatable.hpp"
-#include "common/num_utils.hpp"
-#include "common/numeric_limits.hpp"
 #include "common/string.hpp"
 #include "mac/mac_types.hpp"