优化crc速度

go1_pro_sdk/codec/lowcmd_builder.py

@@ -50,9 +50,12 @@ def build_low_cmd_plain(lowcmd: LowCmd) -> bytes:
     # 20..22 bandWidth BE
     cmd[20:22] = struct.pack('>H', lowcmd.bandWidth)
     # 22..562 motorCmd[20] × 27B
-    motor_bytes = b''.join(m.to_bytes() for m in lowcmd.motorCmd)
-    assert len(motor_bytes) == 540, f'motorCmd 序列化长度错: {len(motor_bytes)}'
-    cmd[22:562] = motor_bytes
+    offset = 22
+    for motor in lowcmd.motorCmd:
+        motor_bytes = motor.to_bytes()
+        assert len(motor_bytes) == 27, f'motorCmd 序列化长度错: {len(motor_bytes)}'
+        cmd[offset:offset + 27] = motor_bytes
+        offset += 27
     # 562..566 bms (默认 0)
     # 566..606 wirelessRemote
     cmd[566:606] = lowcmd.wirelessRemote
@@ -60,7 +63,7 @@ def build_low_cmd_plain(lowcmd: LowCmd) -> bytes:
     cmd[606:610] = lowcmd.reserve
     # 610..612 固定填充 0x0000
     # 612..616 CRC
-    cmd[612:616] = gen_crc(bytes(cmd[:612]))
+    cmd[612:616] = gen_crc(memoryview(cmd)[:612])
 
     return bytes(cmd)
 

go1_pro_sdk/utils/common.py

@@ -15,20 +15,38 @@ import binascii
 
 # ===== CRC32 (用于 LowCmd 末尾 4 字节, PRO 不 XOR, EDU 才 XOR encryptCrc) =====
 
+_CRC32_POLY = 0x04c11db7
+
+
+def _make_crc32_table():
+    table = []
+    for byte in range(256):
+        crc = byte << 24
+        for _ in range(8):
+            if crc & 0x80000000:
+                crc = ((crc << 1) ^ _CRC32_POLY) & 0xFFFFFFFF
+            else:
+                crc = (crc << 1) & 0xFFFFFFFF
+        table.append(crc)
+    return tuple(table)
+
+
+_CRC32_TABLE = _make_crc32_table()
+_CRC_PACK = struct.Struct('<I').pack
+
 def gen_crc(data: bytes) -> bytes:
     """CRC-32 with polynomial 0x04c11db7 (custom 实现, 跟 Unitree MCU 对齐).
 
     跟 Python zlib.crc32 不同 (zlib 用反射 + 0xEDB88320), 所以这个手动实现保留.
     """
+    table = _CRC32_TABLE
     crc = 0xFFFFFFFF
-    for j in struct.unpack("<%dI" % (len(data) // 4), data):
-        for b in range(32):
-            x = (crc >> 31) & 1
-            crc <<= 1
-            crc &= 0xFFFFFFFF
-            if x ^ (1 & (j >> (31 - b))):
-                crc ^= 0x04c11db7
-    return struct.pack('<I', crc)
+    for (word,) in struct.iter_unpack('<I', data):
+        crc = ((crc << 8) & 0xFFFFFFFF) ^ table[((crc >> 24) ^ ((word >> 24) & 0xff)) & 0xff]
+        crc = ((crc << 8) & 0xFFFFFFFF) ^ table[((crc >> 24) ^ ((word >> 16) & 0xff)) & 0xff]
+        crc = ((crc << 8) & 0xFFFFFFFF) ^ table[((crc >> 24) ^ ((word >> 8) & 0xff)) & 0xff]
+        crc = ((crc << 8) & 0xFFFFFFFF) ^ table[((crc >> 24) ^ (word & 0xff)) & 0xff]
+    return _CRC_PACK(crc)
 
 
 # ===== float ↔ hex 字段 (Unitree 用 big-endian float 但小端整数读) =====

tests/test_common.py

@@ -0,0 +1,27 @@
+"""Common codec utility tests."""
+import struct
+
+from go1_pro_sdk.utils.common import gen_crc
+
+
+def _gen_crc_bitwise(data: bytes) -> bytes:
+    crc = 0xFFFFFFFF
+    for (word,) in struct.iter_unpack("<I", data):
+        for bit in range(32):
+            x = (crc >> 31) & 1
+            crc <<= 1
+            crc &= 0xFFFFFFFF
+            if x ^ (1 & (word >> (31 - bit))):
+                crc ^= 0x04c11db7
+    return struct.pack("<I", crc)
+
+
+def test_gen_crc_matches_reference_bitwise():
+    samples = [
+        b"",
+        bytes(4),
+        bytes(range(64)),
+        b"\xfe\xef\xff\x00" + bytes(range(252)) * 2,
+    ]
+    for sample in samples:
+        assert gen_crc(sample) == _gen_crc_bitwise(sample)