fw: add working reed-solomon encoder/decoder

1 files changed, 81 insertions, 0 deletions

diff --git a/controller/fw/tools/reed_solomon.py b/controller/fw/tools/reed_solomon.py
new file mode 100644
index 0000000..9eee6be
--- /dev/null
+++ b/controller/fw/tools/reed_solomon.py
@@ -0,0 +1,81 @@
+import os, sys
+import ctypes as C
+import argparse
+import binascii
+import numpy as np
+import timeit
+import statistics
+
+lib = C.CDLL('rslib.so')
+
+lib.rslib_encode.argtypes = [C.c_int, C.c_size_t, C.POINTER(C.c_char), C.POINTER(C.c_char)]
+lib.rslib_decode.argtypes = [C.c_int, C.c_size_t, C.POINTER(C.c_char)]
+lib.rslib_gexp.argtypes = [C.c_int, C.c_int]
+lib.rslib_gexp.restype = C.c_int
+lib.rslib_decode.restype = C.c_int
+lib.rslib_npar.restype = C.c_size_t
+
+def npar():
+    return lib.rslib_npar()
+
+def encode(data: bytes, nbits=8):
+    out = C.create_string_buffer(len(data) + lib.rslib_npar())
+    lib.rslib_encode(nbits, len(data), data, out)
+    return out.raw
+
+def decode(data: bytes, nbits=8):
+    inout = C.create_string_buffer(data)
+    lib.rslib_decode(nbits, len(data), inout)
+    return inout.raw[:-lib.rslib_npar() - 1]
+
+def cmdline_func_test(args, print=lambda *args, **kwargs: None, benchmark=False):
+    st = np.random.RandomState(seed=args.seed)
+
+    lfsr = [lib.rslib_gexp(i, args.bits) for i in range(2**args.bits - 1)]
+    print('LFSR', len(set(lfsr)), lfsr)
+    assert all(0 < x < 2**args.bits for x in lfsr)
+    assert len(set(lfsr)) == 2**args.bits - 1
+
+    print('Seed', args.seed)
+    for i in range(args.repeat):
+        print(f'Run {i}')
+        test_data = bytes(st.randint(2**args.bits, size=args.message_length, dtype=np.uint8))
+        print('        Raw:', binascii.hexlify(test_data).decode())
+        encoded = encode(test_data, nbits=args.bits)
+        print('     Encoded:', binascii.hexlify(encoded).decode())
+
+        indices = st.permutation(len(encoded))
+        encoded = list(encoded)
+        for pos in indices[:args.errors]:
+            encoded[pos] = st.randint(2**args.bits)
+        encoded = bytes(encoded)
+        print('    Modified:', ''.join(f'\033[91m{b:02x}\033[0m' if pos in indices[:args.errors] else f'{b:02x}' for pos, b in enumerate(encoded)))
+
+        if benchmark:
+            rpt = 10000
+            delta = timeit.timeit('decode(encoded, nbits=args.bits)',
+                    globals={'args': args, 'decode': decode, 'encoded': encoded},
+                    number=rpt)/rpt
+            print(f'Decoding runtime: {delta*1e6:.3f}μs')
+        decoded = decode(encoded, nbits=args.bits)
+        print('     Decoded:', binascii.hexlify(decoded).decode())
+        print('       Delta:', binascii.hexlify(
+                bytes(x^y for x, y in zip(test_data, decoded))
+            ).decode().replace('0', '.'))
+        assert test_data == decoded
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser()
+    cmd_parser = parser.add_subparsers(required=True)
+    test_parser = cmd_parser.add_parser('test', help='Test reed-solomon implementation')
+    test_parser.add_argument('-m', '--message-length', type=int, default=6, help='Test message (plaintext) length in bytes')
+    test_parser.add_argument('-e', '--errors', type=int, default=2, help='Number of byte errors to insert into simulation')
+    test_parser.add_argument('-r', '--repeat', type=int, default=1000, help='Repeat experiment -r times')
+    test_parser.add_argument('-b', '--bits', type=int, default=8, help='Symbol bit size')
+    test_parser.add_argument('-s', '--seed', type=int, default=0, help='Random seed')
+    test_parser.set_defaults(func=cmdline_func_test)
+    enc_parser = cmd_parser.add_parser('encode', help='RS-Encode given hex string')
+    enc_parser.add_argument('hex_str')
+    args = parser.parse_args()
+    args.func(args, print=print)
+