sum: Add sum.py

Author: Expertcoderz

src/sum.py

@@ -0,0 +1,63 @@
+#!/usr/bin/python3
+
+import sys
+from optparse import OptionParser
+
+
+# BSD 16-bit checksum
+def sum_bsd(data: bytes) -> str:
+    checksum = 0
+    for b in data:
+        checksum = (checksum >> 1) + ((checksum & 1) << 15)
+        checksum += b
+        checksum &= 0xFFFF
+
+    return f"{checksum:05}{-(len(data) // -1024):>6}"
+
+
+# SYSV checksum
+def sum_sysv(data: bytes) -> int:
+    s = sum(data)
+    r = s % 2**16 + (s % 2**32) // 2**16
+    checksum = (r % 2**16) + r // 2**16
+
+    return f"{checksum:03} {-(len(data) // -512)}"
+
+
+SUM_ALGORITHMS = {"bsd": sum_bsd, "sysv": sum_sysv}
+
+
+def _sum(opts, filenames: list[str]):
+    for name in filenames:
+        if name == "-":
+            print(SUM_ALGORITHMS[opts.algorithm](sys.stdin.buffer.read()))
+        else:
+            with open(name, "rb") as io:
+                print(f"{SUM_ALGORITHMS[opts.algorithm](io.read())} {name}")
+
+
+if __name__ == "__main__":
+    parser = OptionParser(
+        usage="Usage: %prog [OPTION] [FILE]...", add_help_option=False
+    )
+    parser.add_option("--help", action="help", help="show usage information and exit")
+
+    parser.add_option(
+        "-r",
+        dest="algorithm",
+        action="store_const",
+        const="bsd",
+        default="bsd",
+        help="use the BSD (16-bit) checksum algorithm (1KiB blocks)",
+    )
+    parser.add_option(
+        "-s",
+        dest="algorithm",
+        action="store_const",
+        const="sysv",
+        help="use the System V sum algorithm (512B blocks)",
+    )
+
+    opts, args = parser.parse_args()
+
+    _sum(opts, args or ["-"])