Fix how tap2sna.py handles 0-length pulses in 0/1 bit encodings

In a PZX DATA block, that is.

Author: skoolkid

skoolkit/loadtracer.py

@@ -1,4 +1,4 @@
-# Copyright 2022-2025 Richard Dymond (rjdymond@gmail.com)
+# © 2022-2026 Richard Dymond (rjdymond@gmail.com)
 #
 # This file is part of SkoolKit.
 #
@@ -118,26 +118,19 @@ def get_edges(blocks, first_edge, polarity, analyse=False):
                 one = ','.join(str(d) for d in timings.one)
                 analysis.append(f'{tstates:>10}  {ear:>3}  Data ({data_len} bytes{bits}; {zero}/{one} T-states)')
             start = len(edges) - 1
-            if 0 in timings.zero and 0 in timings.one and sum(timings.zero) == sum(timings.one):
-                # This is sample data as opposed to byte values, so an edge
-                # is the transition between a 0-bit and a 1-bit (or vice versa)
-                sample_t = sum(timings.zero)
-                prev_bit = data[0] & 0x80
-                for k, b in enumerate(data, 1):
-                    for j in range(8 if k < len(data) else timings.used_bits):
-                        if b & 0x80 != prev_bit:
-                            edges.append(tstates)
-                            prev_bit ^= 0x80
-                        tstates += sample_t
-                        b *= 2
-                edges.append(tstates)
-            else:
-                for k, b in enumerate(data, 1):
-                    for j in range(8 if k < len(data) else timings.used_bits):
-                        for d in timings.one if b & 0x80 else timings.zero:
+            p = q = 0
+            for k, b in enumerate(data, 1):
+                for j in range(8 if k < len(data) else timings.used_bits):
+                    for d in timings.one if b & 0x80 else timings.zero:
+                        if d:
                             tstates += d
-                            edges.append(tstates)
-                        b *= 2
+                            if p == q:
+                                edges.append(tstates)
+                                q = 1 - q
+                            else:
+                                edges[-1] += d
+                        p = 1 - p
+                    b *= 2
 
             # Tail pulse
             if timings.tail:

sphinx/source/changelog.rst

@@ -34,6 +34,8 @@ Changelog
   :ref:`ref-AudioWriter` section
 * Fixed the bug in CSimulator that restricts the ``timeout`` simulated load
   configuration parameter to a maximum value of 1227 seconds
+* Fixed how :ref:`tap2sna.py` handles zero-length pulses in the encodings of 0s
+  and 1s in a PZX DATA block
 
 9.6 (2025-05-12)
 ----------------

tests/test_tap2sna.py

@@ -748,7 +748,7 @@ def test_option_tape_analysis_pzx_file(self):
         pzx.add_puls(pulse_counts=((5000, 2168), (1, 430), (1, 870)))
         pzx.add_data((11, 12, 13, 14, 15), (570, 570), (1050, 1050), tail=0, used_bits=5, polarity=0)
         pzx.add_puls(pulse_counts=((2000, 1234), (2, 500), (1, 1000)))
-        pzx.add_data((255, 0, 255, 0, 254), (80, 0), (0, 80), tail=0)
+        pzx.add_data((255, 0, 255, 0, 255), (80, 0), (0, 80), tail=0)
         pzx.add_puls(pulses=(0, 1000, 1000, 1000))
         pzxfile = self.write_bin_file(pzx.data, suffix='.pzx')
         output, error = self.run_tap2sna(f'--tape-analysis {pzxfile}', catch_exit=0)