X-Git-Url: http://git.droids-corp.org/?p=aversive.git;a=blobdiff_plain;f=projects%2Fmicrob2010%2Ftests%2Fstatic_beacon%2Fcksum.py;fp=projects%2Fmicrob2010%2Ftests%2Fstatic_beacon%2Fcksum.py;h=38d6634d16b40dcfc17aa81b0d4f2f97a6224fa3;hp=0000000000000000000000000000000000000000;hb=d992c7dd579170e226cfceabb652cdda6edb97b4;hpb=844fa3427676e08d7e9f92279788def635377714

diff --git a/projects/microb2010/tests/static_beacon/cksum.py b/projects/microb2010/tests/static_beacon/cksum.py
new file mode 100644
index 0000000..38d6634
--- /dev/null
+++ b/projects/microb2010/tests/static_beacon/cksum.py
@@ -0,0 +1,51 @@
+#!/usr/bin/python
+
+import random
+
+# val is 12 bits. Return the 16 bits value that includes the 4 bits
+# cksum in MSB.
+def do_cksum(val):
+    x = (val & 0xfff)
+    # add the three 4-bits blocks of x together
+    cksum = x & 0xf
+    x = x >> 4
+    cksum += x & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    x = x >> 4
+    cksum += x & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    cksum = (~cksum) & 0xf
+    return (cksum << 12) + (val & 0xfff)
+
+# val is 16 bits, including 4 bits-cksum in MSB, return 0xFFFF is cksum
+# is wrong, or the 12 bits value on success.
+def verify_cksum(val):
+    x = (val & 0xfff)
+    # add the four 4-bits blocks of val together
+    cksum = val & 0xf
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    if cksum == 0xf:
+        return x
+    return 0xffff # wrong value
+
+
+
+err = 0
+total = 0
+for i in range(200):
+    x = random.randint(0,(1<<12)-1)
+    y = do_cksum(x)
+    y = random.randint(0,(1<<16)-1)
+    z = verify_cksum(y)
+    if z == 0xffff:
+        err += 1
+    total += 1
+print "%d errors / %d"%(err, total)