Add tablecheck.py to the repo.

2 files changed, 52 insertions, 0 deletions

diff --git a/devtools/README b/devtools/README
index 4a16a5b0..7647317b 100644
--- a/devtools/README
+++ b/devtools/README
@@ -78,6 +78,9 @@ May be useful for comparing logs when regression tests break.
 Strip leading comment lines from NMEA sentence logs.  gpsfake can do
 this itself now, so this script has a lot of dust on it. 
 
+== tablecheck.py ==
 
+Redo bit offsets of AIVDM message layout tables to be conformant with list 
+lengths.
 
 
diff --git a/devtools/tablecheck.py b/devtools/tablecheck.py
new file mode 100755
index 00000000..3f48dc0d
--- /dev/null
+++ b/devtools/tablecheck.py
@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+#
+# Compute offsets for an AIVDM message breakdown, given the bit widths.
+# Takes a single argument, the line number of a table start.
+# Writes the corrected table to standard output.
+
+import sys
+
+if __name__ == '__main__':
+    startline = int(sys.argv[1])
+
+    table = []
+    keep = False
+    i = 0
+    for line in sys.stdin:
+        i += 1
+        if i == startline:
+            if line.startswith("|="):
+                keep = True
+            else:
+                print >>sys.stderr, "Bad table start"
+                sys.exit(1)
+        elif line.startswith("|="):
+            keep = False
+        if keep:
+            table.append(line)
+    table = table[2:]
+
+    widths = map(lambda s: s.split('|')[2].strip(), table)
+
+    offsets = []
+    base = 0
+    for w in widths:
+        if not w:
+            offsets.append('')
+        else:
+            w = int(w)
+            offsets.append("%d-%d" % (base, base + w - 1))
+            base += w
+    print >>sys.stderr, "Total bits:", base 
+    owidth = max(*map(len, offsets)) 
+    for (i, off) in enumerate(offsets):
+        offsets[i] += " " * (owidth - len(offsets[i]))
+    
+    for (i, t) in enumerate(table):
+        print "|" + offsets[i] + t[owidth+1:].rstrip()
+
+
+