util: introduce libscrc as optional dependency

As discussed in #85 libscrc can
increase the speed of CRC calculation. However, as it is C-based module,
the usage of it is made optional to cope with the environment without
Python development package.

README.md

@@ -37,12 +37,17 @@ page](https://github.com/fgsect/scat/wiki/Baseband-Dumps) for details.
 Install SCAT through pip using:
 
 ```
+# If you want fast CRC calculation (for Qualcomm and HiSilicon)
+$ pip install "scat[fastcrc] @ git+https://github.com/fgsect/scat"
+
+# If you don't want or can't build libscrc
 $ pip install https://github.com/fgsect/scat
 ```
 
 Please note that the name SCAT is taken in the PyPI, I will find further solution.
 
-For development purposes, please use `pip install -e .` on your checkout directory.
+For development purposes, please use `pip install -e .[fastcrc]` or `pip install
+-e .` on your checkout directory.
 The older `scat.py` is moved to `src/scat/main.py`.
 
 ## Usage
@@ -76,7 +81,7 @@ please file an issue with the debug output (`--debug`) attached:
 
 SCAT version up to 1.1.0 required specifying the Samsung baseband type manually
 using `-m`. As SCAT now autodetects the Samsung baseband type, This option will
-be deprecated in future releases.
+be deprecated in SCAT 1.2.0, and may be removed in SCAT >= 2.0.0.
 
 ### USB
 Accessing the baseband diagnostics via USB:

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "scat"
-version = "1.0.0"
+version = "1.1.0"
 authors = [
     { name="Shinjo Park", email="[email protected]" },
 ]
@@ -16,6 +16,10 @@ dependencies = [
     "pyusb>=1.0.2",
     "pyserial>=3.3"
 ]
+[project.optional-dependencies]
+fastcrc = [
+    "libscrc>=1.8.0",
+]
 
 [project.urls]
 "Homepage" = "https://github.com/fgsect/scat"

src/scat/util.py

@@ -6,6 +6,11 @@
 import sys
 import string
 from enum import IntEnum, unique
+try:
+    import libscrc
+    has_libscrc = True
+except ModuleNotFoundError:
+    has_libscrc = False
 
 XXD_SET = string.ascii_letters + string.digits + string.punctuation
 
@@ -45,10 +50,13 @@
     ]
 
 def dm_crc16(arr):
-    ret = 0xffff
-    for b in arr:
-        ret = (ret >> 8) ^ crc_table[(ret ^ b) & 0xff]
-    return ret ^ 0xffff
+    if has_libscrc:
+        return libscrc.x25(arr)
+    else:
+        ret = 0xffff
+        for b in arr:
+            ret = (ret >> 8) ^ crc_table[(ret ^ b) & 0xff]
+        return ret ^ 0xffff
 
 def wrap(arr):
     t = arr.replace(b'\x7d', b'\x7d\x5d')