Merge pull request #25 from zacharytomlinson/zacharytomlinson-crc-adhoc

CRC adhoc

Author: well-it-wasnt-me

example.py

@@ -20,6 +20,7 @@
 )
 
 print(sas.start())
+print(sas.en_dis_rt_event_reporting(False))
 print(sas.sas_version_gaming_machine_serial_id())
 print(sas.gaming_machine_id())
 print(sas.aft_in(15.00))

sas.py

@@ -6,7 +6,7 @@
 import logging
 import datetime
 
-from PyCRC.CRC16Kermit import CRC16Kermit
+from utils import Crc
 from multiprocessing import log_to_stderr
 
 from models import *
@@ -47,7 +47,7 @@ def __init__(
         self.pos_id = pos_id
         self.transaction = None
         self.my_key = key
-        self.poll_address = poll_address
+        self.poll_address= poll_address
         self.perpetual = perpetual
 
         # Init the Logging system
@@ -139,7 +139,7 @@ def open(self):
             raise SASOpenError
 
     def _conf_event_port(self):
-        """Do magick to make SAS Happy and work with their effing parity"""
+        """Do magick to make SAS Happy and work with their effing wakeup bit"""
         self.open()
         self.connection.flush()
         self.connection.timeout = self.poll_timeout
@@ -167,8 +167,7 @@ def _send_command(
             buf_header.extend(command)
 
             if crc_need:
-                crc = CRC16Kermit().calculate(bytearray(buf_header).decode("utf-8"))
-                buf_header.extend([((crc >> 8) & 0xFF), (crc & 0xFF)])
+                buf_header.extend(Crc.calculate(bytes(buf_header)))
 
             self.connection.write([self.poll_address, self.address])
 
@@ -210,12 +209,10 @@ def _check_response(rsp):
         if rsp == "":
             raise NoSasConnection
 
-        tmp_crc = binascii.hexlify(rsp[-2:])
-        crc1 = CRC16Kermit().calculate(rsp[0:-2])
-        crc1 = hex(crc1).zfill(4)
-        crc1 = bytes(crc1, "utf-8")[2:]
+        mac_crc = [int.from_bytes(rsp[-2:-1]), int.from_bytes(rsp[-1:])]
+        my_crc = Crc.calculate(rsp[0:-2])
 
-        if tmp_crc != crc1:
+        if mac_crc != my_crc:
             raise BadCRC(binascii.hexlify(rsp))
         else:
             return rsp[1:-2]

utils/Crc.py

@@ -0,0 +1,65 @@
+from enum import Enum
+from ctypes import c_ushort
+
+MAGIC_SEED = 0x8408
+table = []
+
+
+class Endianness(Enum):
+    LITTLE_ENDIAN = 0
+    BIG_ENDIAN = 1
+
+
+for i in range(0, 256):
+    val = c_ushort(i).value
+    for j in range(0, 8):
+        val = c_ushort(val >> 1).value ^ MAGIC_SEED if val & 0x0001 else c_ushort(val >> 1).value
+    table.append(hex(val))
+
+
+def calculate(payload=None, init=0, sigbit=Endianness.LITTLE_ENDIAN):
+    _crc = init
+
+    for c in payload:
+        q = _crc ^ c
+        _crc = c_ushort(_crc >> 8).value ^ int(table[(q & 0x00ff)], 0)
+
+    if sigbit == Endianness.BIG_ENDIAN:
+        _crc = (_crc & 0x00ff) << 8 | (_crc & 0xff00) >> 8
+    else:
+        _crc = (_crc & 0xff00) >> 8 | (_crc & 0x00ff) << 8
+
+    return [((_crc >> 8) & 0xFF), (_crc & 0xFF)]
+
+
+''' Tableless algo in Python and Rust
+def calculate(payload: bytes, init=0, sigbit=Endianness.LITTLE_ENDIAN):
+    crc, y = init, 0
+
+    for byte in payload:
+        x = c_ushort(byte)
+        y = (crc ^ int(x)) & 0o17
+        crc = (crc >> 8) ^ (y * MAGIC_SEED)
+        y = (crc ^ (x >> 8)) & 0o17
+        crc = (crc >> 8) ^ (y * MAGIC_SEED)
+
+    if sigbit == Endianness.BIG_ENDIAN:
+        return crc & 0xFF, (crc >> 8) & 0xFF
+
+    return (crc >> 8) & 0xFF, crc & 0xFF
+
+fn crc16(msg: &[u8]) -> u16 {
+    let mut crc: u16 = 0;
+    let (mut c, mut q): (u16, u16);
+
+    for byte in msg.iter() {
+        c = *byte as u16;
+        q = (crc ^ c) & 0o17;
+        crc = (crc >> 4) ^ (q * 0o10201);
+        q = (crc ^ (c >> 4)) & 0o17;
+        crc = (crc >> 4) ^ (q * 0o10201);
+    }
+
+    crc
+}
+'''