Add FNV-1a hash functions (#12502)

esphome/core/helpers.cpp

@@ -143,17 +143,29 @@ uint16_t crc16be(const uint8_t *data, uint16_t len, uint16_t crc, uint16_t poly,
   return refout ? (crc ^ 0xffff) : crc;
 }
 
+// FNV-1 hash - deprecated, use fnv1a_hash() for new code
 uint32_t fnv1_hash(const char *str) {
-  uint32_t hash = 2166136261UL;
+  uint32_t hash = FNV1_OFFSET_BASIS;
   if (str) {
     while (*str) {
-      hash *= 16777619UL;
+      hash *= FNV1_PRIME;
       hash ^= *str++;
     }
   }
   return hash;
 }
 
+// FNV-1a hash - preferred for new code
+uint32_t fnv1a_hash_extend(uint32_t hash, const char *str) {
+  if (str) {
+    while (*str) {
+      hash ^= *str++;
+      hash *= FNV1_PRIME;
+    }
+  }
+  return hash;
+}
+
 float random_float() { return static_cast<float>(random_uint32()) / static_cast<float>(UINT32_MAX); }
 
 // Strings

esphome/core/helpers.h

@@ -378,9 +378,24 @@ uint16_t crc16be(const uint8_t *data, uint16_t len, uint16_t crc = 0, uint16_t p
                  bool refout = false);
 
 /// Calculate a FNV-1 hash of \p str.
+/// Note: FNV-1a (fnv1a_hash) is preferred for new code due to better avalanche characteristics.
 uint32_t fnv1_hash(const char *str);
 inline uint32_t fnv1_hash(const std::string &str) { return fnv1_hash(str.c_str()); }
 
+/// FNV-1 32-bit offset basis
+constexpr uint32_t FNV1_OFFSET_BASIS = 2166136261UL;
+/// FNV-1 32-bit prime
+constexpr uint32_t FNV1_PRIME = 16777619UL;
+
+/// Extend a FNV-1a hash with additional string data.
+uint32_t fnv1a_hash_extend(uint32_t hash, const char *str);
+inline uint32_t fnv1a_hash_extend(uint32_t hash, const std::string &str) {
+  return fnv1a_hash_extend(hash, str.c_str());
+}
+/// Calculate a FNV-1a hash of \p str.
+inline uint32_t fnv1a_hash(const char *str) { return fnv1a_hash_extend(FNV1_OFFSET_BASIS, str); }
+inline uint32_t fnv1a_hash(const std::string &str) { return fnv1a_hash(str.c_str()); }
+
 /// Return a random 32-bit unsigned integer.
 uint32_t random_uint32();
 /// Return a random float between 0 and 1.

tests/integration/fixtures/fnv1a_hash.yaml

@@ -0,0 +1,60 @@
+esphome:
+  name: fnv1a-hash-test
+  platformio_options:
+    build_flags:
+      - "-DDEBUG"
+  on_boot:
+    - lambda: |-
+        using esphome::fnv1a_hash;
+        using esphome::fnv1a_hash_extend;
+
+        // Test empty string (should return offset basis)
+        uint32_t hash_empty = fnv1a_hash("");
+        if (hash_empty == 0x811c9dc5) {
+          ESP_LOGI("FNV1A", "empty PASSED");
+        } else {
+          ESP_LOGE("FNV1A", "empty FAILED: 0x%08x != 0x811c9dc5", hash_empty);
+        }
+
+        // Test known FNV-1a hashes
+        uint32_t hash_hello = fnv1a_hash("hello");
+        if (hash_hello == 0x4f9f2cab) {
+          ESP_LOGI("FNV1A", "known_hello PASSED");
+        } else {
+          ESP_LOGE("FNV1A", "known_hello FAILED: 0x%08x != 0x4f9f2cab", hash_hello);
+        }
+
+        uint32_t hash_helloworld = fnv1a_hash("helloworld");
+        if (hash_helloworld == 0x3b9f5c61) {
+          ESP_LOGI("FNV1A", "known_helloworld PASSED");
+        } else {
+          ESP_LOGE("FNV1A", "known_helloworld FAILED: 0x%08x != 0x3b9f5c61", hash_helloworld);
+        }
+
+        // Test fnv1a_hash_extend consistency
+        uint32_t hash1 = fnv1a_hash("hello");
+        hash1 = fnv1a_hash_extend(hash1, "world");
+        uint32_t hash2 = fnv1a_hash("helloworld");
+
+        if (hash1 == hash2) {
+          ESP_LOGI("FNV1A", "extend PASSED");
+        } else {
+          ESP_LOGE("FNV1A", "extend FAILED: 0x%08x != 0x%08x", hash1, hash2);
+        }
+
+        // Test with std::string
+        std::string str1 = "foo";
+        std::string str2 = "bar";
+        uint32_t hash3 = fnv1a_hash(str1);
+        hash3 = fnv1a_hash_extend(hash3, str2);
+        uint32_t hash4 = fnv1a_hash("foobar");
+
+        if (hash3 == hash4) {
+          ESP_LOGI("FNV1A", "string PASSED");
+        } else {
+          ESP_LOGE("FNV1A", "string FAILED: 0x%08x != 0x%08x", hash3, hash4);
+        }
+
+host:
+api:
+logger:

tests/integration/test_fnv1a_hash.py

@@ -0,0 +1,69 @@
+"""Integration test for FNV-1a hash functions."""
+
+from __future__ import annotations
+
+import asyncio
+import re
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_fnv1a_hash(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that FNV-1a hash functions work correctly."""
+
+    test_results = {}
+    all_tests_complete = asyncio.Event()
+    expected_tests = {"empty", "known_hello", "known_helloworld", "extend", "string"}
+
+    def on_log_line(line: str) -> None:
+        """Capture log lines with test results."""
+        # Strip ANSI escape codes
+        clean_line = re.sub(r"\x1b\[[0-9;]*m", "", line)
+        # Look for our test result messages
+        # Format: "[timestamp][level][FNV1A:line]: test_name PASSED"
+        match = re.search(r"\[FNV1A:\d+\]:\s+(\w+)\s+(PASSED|FAILED)", clean_line)
+        if match:
+            test_name = match.group(1)
+            result = match.group(2)
+            test_results[test_name] = result
+            if set(test_results.keys()) >= expected_tests:
+                all_tests_complete.set()
+
+    async with (
+        run_compiled(yaml_config, line_callback=on_log_line),
+        api_client_connected() as client,
+    ):
+        device_info = await client.device_info()
+        assert device_info is not None
+        assert device_info.name == "fnv1a-hash-test"
+
+        # Wait for all tests to complete or timeout
+        try:
+            await asyncio.wait_for(all_tests_complete.wait(), timeout=2.0)
+        except TimeoutError:
+            pytest.fail(f"Tests timed out. Got results for: {set(test_results.keys())}")
+
+        # Verify all tests passed
+        assert "empty" in test_results, "empty string test not found"
+        assert test_results["empty"] == "PASSED", "empty string test failed"
+
+        assert "known_hello" in test_results, "known_hello test not found"
+        assert test_results["known_hello"] == "PASSED", "known_hello test failed"
+
+        assert "known_helloworld" in test_results, "known_helloworld test not found"
+        assert test_results["known_helloworld"] == "PASSED", (
+            "known_helloworld test failed"
+        )
+
+        assert "extend" in test_results, "fnv1a_hash_extend test not found"
+        assert test_results["extend"] == "PASSED", "fnv1a_hash_extend test failed"
+
+        assert "string" in test_results, "std::string test not found"
+        assert test_results["string"] == "PASSED", "std::string test failed"