From d2323a8f3b22a12808b855da4b2f9c8ce5864df7 Mon Sep 17 00:00:00 2001
From: Chen Peng <pizer.chen@gmail.com>
Date: Mon, 10 Aug 2026 12:05:34 +0800
Subject: [PATCH] =?UTF-8?q?=E7=A1=AE=E4=BF=9D=20capacity=20ispow2?=
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---
 cKit/Foundation/c_FastByteRingBuffer.c   | 18 ++++++++++++++++--
 cKit/Foundation/c_FastByteRingBuffer.t.c |  3 ++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/cKit/Foundation/c_FastByteRingBuffer.c b/cKit/Foundation/c_FastByteRingBuffer.c
index e7dffe3..27820a9 100644
--- a/cKit/Foundation/c_FastByteRingBuffer.c
+++ b/cKit/Foundation/c_FastByteRingBuffer.c
@@ -22,14 +22,28 @@ c_size_t round_up_to_pow2(c_size_t v) {
     return v;
 }
 
+C_STATIC_FORCE_INLINE
+c_bool_t c_FastByteRingBuffer_IsPow2(c_size_t capacity) {
+    // A power of 2 must be greater than zero.
+    // The bitwise trick (capacity & (capacity - 1)) works because a power of 2
+    // has exactly one bit set (e.g., 01000). Subtracting 1 flips all bits up to
+    // that set bit (e.g., 00111). Performing a bitwise AND yields exactly 0.
+    if (capacity == 0) {
+        return C_FALSE;
+    }
+    return ((capacity & (capacity - 1)) == 0) ? C_TRUE : C_FALSE;
+}
+
 /* ------------------------------------------------------------------------------------------------------------------ */
 /*  */
 
 c_err_t c_FastByteRingBuffer_Init(c_FastByteRingBuffer_t* self, c_size_t capacity) {
     if (!self || capacity == 0) return C_ERR_PARAM;
-
+    if (!c_FastByteRingBuffer_IsPow2(capacity)) {
+        return C_ERR_PARAM;
+    }
     // 自動向上對齊，確保符合 Power of Two
-    self->capacity = round_up_to_pow2(capacity);
+    self->capacity = capacity;
     self->mask = self->capacity - 1; // 建立遮罩
     self->head = 0;
     self->tail = 0;
diff --git a/cKit/Foundation/c_FastByteRingBuffer.t.c b/cKit/Foundation/c_FastByteRingBuffer.t.c
index 63e0189..0444190 100644
--- a/cKit/Foundation/c_FastByteRingBuffer.t.c
+++ b/cKit/Foundation/c_FastByteRingBuffer.t.c
@@ -244,8 +244,9 @@ static void test_conditional_is_validator(void) {
 
 static void test_ring_buffer_memcmp(void) {
     c_FastByteRingBuffer_t ring;
-    assert(c_FastByteRingBuffer_Init(&ring, 6) == C_SUCCESS); // Capacity = 6
+    assert(c_FastByteRingBuffer_Init(&ring, 6) == C_ERR_INVALID_PARAM); // Capacity = 6
 
+    assert(c_FastByteRingBuffer_Init(&ring, 8) == C_SUCCESS); // Capacity = 6
     uint8_t payload[] = {0x00, 0x11, 0x22, 0x33};
     c_FastByteRingBuffer_WriteBuffer(&ring, payload, 4);