pdtest: use less expensive Python routine to get text differences

Python ships with a difflib(3) module which is used in the pdtest(1)
utility. The Differ.compare() routine is rather expensive, especially
when the set of input text becomes "large" (a few thousand lines). Use
the less expensive unified_diff() routine instead which does not suffer
from that cost. From the sigrok-test perspective the resulting data is
as usable.

1 files changed, 4 insertions, 7 deletions

diff --git a/decoder/pdtest b/decoder/pdtest
index e3509b9..5948325 100755
--- a/decoder/pdtest
+++ b/decoder/pdtest
@@ -24,7 +24,7 @@ import re
 from getopt import getopt
 from tempfile import mkstemp
 from subprocess import Popen, PIPE
-from difflib import Differ
+from difflib import unified_diff
 from hashlib import md5
 from shutil import copy
 
@@ -236,12 +236,9 @@ def get_tests(testnames):
 def diff_text(f1, f2):
     t1 = open(f1).readlines()
     t2 = open(f2).readlines()
-    diff = []
-    d = Differ()
-    for line in d.compare(t1, t2):
-        if line[:2] in ('- ', '+ '):
-            diff.append(line.strip())
-
+    diff = list(unified_diff(t1, t2))
+    diff = diff[2:] # Strip two from/to filename lines with "+++"/"---".
+    diff = [d.strip() for d in diff if d[0] in ('+', '-')]
     return diff