[rp2040] Use SmallBufferWithHeapFallback for preferences

esphome/components/rp2040/preferences.cpp

@@ -8,7 +8,6 @@
 #include "preferences.h"
 
 #include <cstring>
-#include <vector>
 
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
@@ -25,6 +24,9 @@ static bool s_flash_dirty = false;          // NOLINT(cppcoreguidelines-avoid-no
 
 static const uint32_t RP2040_FLASH_STORAGE_SIZE = 512;
 
+// Stack buffer size for preferences - covers virtually all real-world preferences without heap allocation
+static constexpr size_t PREF_BUFFER_SIZE = 64;
+
 extern "C" uint8_t _EEPROM_start;
 
 template<class It> uint8_t calculate_crc(It first, It last, uint32_t type) {
@@ -42,12 +44,14 @@ class RP2040PreferenceBackend : public ESPPreferenceBackend {
   uint32_t type = 0;
 
   bool save(const uint8_t *data, size_t len) override {
-    std::vector<uint8_t> buffer;
-    buffer.resize(len + 1);
-    memcpy(buffer.data(), data, len);
-    buffer[buffer.size() - 1] = calculate_crc(buffer.begin(), buffer.end() - 1, type);
+    const size_t buffer_size = len + 1;
+    SmallBufferWithHeapFallback<PREF_BUFFER_SIZE> buffer_alloc(buffer_size);
+    uint8_t *buffer = buffer_alloc.get();
 
-    for (uint32_t i = 0; i < len + 1; i++) {
+    memcpy(buffer, data, len);
+    buffer[len] = calculate_crc(buffer, buffer + len, type);
+
+    for (size_t i = 0; i < buffer_size; i++) {
       uint32_t j = offset + i;
       if (j >= RP2040_FLASH_STORAGE_SIZE)
         return false;
@@ -60,22 +64,23 @@ class RP2040PreferenceBackend : public ESPPreferenceBackend {
     return true;
   }
   bool load(uint8_t *data, size_t len) override {
-    std::vector<uint8_t> buffer;
-    buffer.resize(len + 1);
+    const size_t buffer_size = len + 1;
+    SmallBufferWithHeapFallback<PREF_BUFFER_SIZE> buffer_alloc(buffer_size);
+    uint8_t *buffer = buffer_alloc.get();
 
-    for (size_t i = 0; i < len + 1; i++) {
+    for (size_t i = 0; i < buffer_size; i++) {
       uint32_t j = offset + i;
       if (j >= RP2040_FLASH_STORAGE_SIZE)
         return false;
       buffer[i] = s_flash_storage[j];
     }
 
-    uint8_t crc = calculate_crc(buffer.begin(), buffer.end() - 1, type);
-    if (buffer[buffer.size() - 1] != crc) {
+    uint8_t crc = calculate_crc(buffer, buffer + len, type);
+    if (buffer[len] != crc) {
       return false;
     }
 
-    memcpy(data, buffer.data(), len);
+    memcpy(data, buffer, len);
     return true;
   }
 };