update README, nicer output from reducer

README.md

@@ -144,6 +144,58 @@ memory during a test, if that memory would not be freed on a test
 failure.  This will leak memory and libFuzzer will run out of memory
 very quickly in each fuzzing session.
 
+## Test case reduction
+
+While tests generated by symbolic execution are likely to be highly
+concise already, fuzzer-generated tests may be much larger than they
+need to be.
+
+DeepState provides a test case reducer to shrink tests intelligently,
+aware of the structure of a DeepState test.  For example, if your
+executable is named `TestFileSystem` and the test you want to reduce
+is named `rmdirfail.test` you would use it like this:
+
+```shell
+deepstate-reduce ./TestFileSystem rmdirfail.test minrmdirfail.test
+```
+
+In many cases, this will result in finding a different failure or
+crash that allow smaller test cases, so you can also provide a string
+that controls which test outputs are considered valid reductions (by
+default, the reducer looks for any test that fails or crashes):
+
+```shell
+deepstate-reduce ./TestFileSystem rmdirfail.test minrmdirfail.test "FATAL: /root/testfs/super.c(252)"
+```
+
+The output will look something like:
+```shell
+ORIGINAL TEST HAS 119 BYTES
+LAST BYTE READ IS 123
+ONEOF REMOVAL REDUCED TEST TO 103 BYTES
+BYTE REDUCTION: BYTE 3 FROM 4 TO 0
+BYTE REDUCTION: BYTE 7 FROM 2 TO 1
+BYTE REDUCTION: BYTE 15 FROM 3 TO 2
+BYTE REDUCTION: BYTE 19 FROM 4 TO 0
+BYTE REDUCTION: BYTE 55 FROM 3 TO 1
+BYTE REDUCTION: BYTE 59 FROM 2 TO 0
+BYTE REDUCTION: BYTE 75 FROM 2 TO 0
+BYTE REDUCTION: BYTE 79 FROM 4 TO 0
+ONEOF REMOVAL REDUCED TEST TO 91 BYTES
+BYTE REDUCTION: BYTE 59 FROM 4 TO 0
+ONEOF REMOVAL REDUCED TEST TO 87 BYTES
+ONEOF REMOVAL REDUCED TEST TO 75 BYTES
+ONEOF REMOVAL REDUCED TEST TO 55 BYTES
+ONEOF REMOVAL REDUCED TEST TO 51 BYTES
+NO REDUCTIONS FOUND
+PADDING TEST WITH 5 ZEROS
+
+WRITING REDUCED TEST TO minrmdirfail.test
+```
+
+You can use `--which <testname>` to specify which test to
+run, as with the `--input_which_test` options to test replay.
+
 ## Fuzzing with AFL
 
 DeepState can also be used with a file-based fuzzer (e.g. AFL).  There

bin/deepstate/reducer.py

@@ -127,7 +127,10 @@ def main():
         print "PADDING TEST WITH", (s[1] + 1) - len(currentTest), "ZEROS"
         padding = bytearray('\x00' * ((s[1] + 1) - len(currentTest)))
         currentTest = currentTest + padding
-
+    
+    print
+    print "WRITING REDUCED TEST TO", out
+        
     with open(out, 'wb') as outf:
         outf.write(currentTest)