Share the object id hash loop with the flash name path

esphome/core/entity_base.cpp

@@ -14,17 +14,6 @@ ESPHOME_LOG_TAG(TAG, "entity_base");
 
 #ifdef USE_ESP8266
 namespace {
-// fnv1_hash_object_id() for a name in flash
-uint32_t fnv1_hash_object_id_progmem(const char *str, size_t len) {
-  uint32_t hash = FNV1_OFFSET_BASIS;
-  for (size_t i = 0; i < len; i++) {
-    hash *= FNV1_PRIME;
-    char c = static_cast<char>(progmem_read_byte(reinterpret_cast<const uint8_t *>(str + i)));
-    hash ^= static_cast<uint8_t>(to_sanitized_char(to_snake_case_char(c)));
-  }
-  return hash;
-}
-
 // RAM copies made by get_name(), only for entities whose name is asked for
 struct NameCopy {
   NameCopy *next;
@@ -82,11 +71,11 @@ void EntityBase::configure_entity_(const char *name, uint32_t object_id_hash, ui
     this->flags_.has_own_name = true;
     // Static name - codegen precomputes the hash; external register_* callers may pass 0
     if (object_id_hash == 0) {
-#ifdef USE_ESP8266
-      object_id_hash = fnv1_hash_object_id_progmem(this->name_.progmem_ptr(), this->name_.size());
-#else
-      object_id_hash = fnv1_hash_object_id(this->name_.progmem_ptr(), this->name_.size());
-#endif
+      // The name is in flash on ESP8266, so read it byte by byte through progmem_read_byte()
+      const char *name_p = this->name_.progmem_ptr();
+      object_id_hash = fnv1_hash_object_id(this->name_.size(), [name_p](size_t i) {
+        return static_cast<char>(progmem_read_byte(reinterpret_cast<const uint8_t *>(name_p + i)));
+      });
     }
     this->object_id_hash_ = object_id_hash;
   }

esphome/core/helpers.h

@@ -1133,17 +1133,21 @@ template<size_t N> inline char *str_sanitize_to(char (&buffer)[N], const char *s
 
 /// Calculate FNV-1 hash of a string while applying snake_case + sanitize transformations.
 /// This computes object_id hashes directly from names without creating an intermediate buffer.
+/// read_byte(i) returns character i, so a name in flash can be hashed through progmem_read_byte().
 /// IMPORTANT: Must match Python fnv1_hash_object_id() in esphome/helpers.py.
 /// If you modify this function, update the Python version and tests in both places.
-inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
+template<typename ReadByte> inline uint32_t fnv1_hash_object_id(size_t len, ReadByte read_byte) {
   uint32_t hash = FNV1_OFFSET_BASIS;
   for (size_t i = 0; i < len; i++) {
     hash *= FNV1_PRIME;
     // Apply snake_case (space->underscore, uppercase->lowercase) then sanitize
-    hash ^= static_cast<uint8_t>(to_sanitized_char(to_snake_case_char(str[i])));
+    hash ^= static_cast<uint8_t>(to_sanitized_char(to_snake_case_char(read_byte(i))));
   }
   return hash;
 }
+inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
+  return fnv1_hash_object_id(len, [str](size_t i) { return str[i]; });
+}
 
 #ifdef USE_ESP8266
 // ESP8266: Use vsnprintf_P to keep format strings in flash (PROGMEM)

tests/components/core/test_entity_base_name.cpp

@@ -2,6 +2,7 @@
 
 #include "esphome/core/entity_base.h"
 
+#include <cstring>
 #include <type_traits>
 #include <utility>
 
@@ -24,6 +25,17 @@ TEST(EntityBaseName, ZeroHashIsComputedFromTheName) {
   EXPECT_EQ(entity.get_object_id_hash(), fnv1_hash_object_id("Living Room Temp", 16));
 }
 
+// The values come from the Python fnv1_hash_object_id() test table. Reading through the byte
+// reader is the path a name in flash takes on ESP8266.
+TEST(EntityBaseName, HashThroughByteReaderMatchesPlainHash) {
+  const char *name = "My Sensor Name";
+  const size_t len = strlen(name);
+  const uint32_t expected = 0x2760962A;
+  EXPECT_EQ(fnv1_hash_object_id(name, len), expected);
+  EXPECT_EQ(fnv1_hash_object_id(len, [name](size_t i) { return name[i]; }), expected);
+  EXPECT_EQ(fnv1_hash_object_id(0, [](size_t) { return 'x'; }), 0x811C9DC5u);
+}
+
 TEST(EntityBaseName, PrecomputedHashIsKept) {
   TestEntity entity;
   entity.configure("Living Room Temp", 0x1234);