The shader split reads each SARC member's name up to its own NUL

dm/gfx/tools/shader_split.py

@@ -2117,7 +2117,8 @@ def sarc_members(d, label='SARC'):
     for i in range(n):
         h, attr, s, e = struct.unpack_from('<IIII', d, hl + 12 + 16 * i)
         if not s <= e <= len(d) - doff: red(f'{label}: SARC member {i} at {s:#x}..{e:#x} of the data lies outside its {len(d) - doff:#x} bytes')
-        nm = d[names + (attr & 0xffffff) * 4:].split(b'\0')[0].decode('utf-8', 'replace') if attr >> 24 else f'#{i}'
+        o = names + (attr & 0xffffff) * 4; z = d.find(b'\0', o)   # up to the name's own NUL: splitting the rest of the archive per member was quadratic (Fire Emblem Fortune's Weave's Layout/Common.arc.zst: 6 minutes)
+        nm = d[o:z if z >= 0 else len(d)].decode('utf-8', 'replace') if attr >> 24 else f'#{i}'
         yield nm, d[doff + s:doff + e]
 
 NV_STAGES = ['vs', 'ps', 'gs', 'hs', 'ds', 'cs']   # NVN stage order

dm/tools/tests/test_split_nesting.py

@@ -74,5 +74,15 @@ def test_yaz0_expansion_is_charged_before_it_is_decoded(self):
         self.assertEqual(dec.call_count, 0)
 
 
+class MemberNames(unittest.TestCase):
+    def test_names_and_time(self):   # each name ends at its own NUL; splitting the rest of the archive per member made Fire Emblem Fortune's Weave's 9.8 MB layout SARC take 6 minutes
+        members = [(b'tex%04d.bntx' % i, bytes(0x4000)) for i in range(800)]
+        import time
+        archive = fz.sarc(members)   # built outside the timing: only the member reading is measured (about 1 ms here, 47 s with the per-member split)
+        t = time.monotonic(); got = list(ss.sarc_members(archive)); took = time.monotonic() - t
+        self.assertEqual(got, [(n.decode(), m) for n, m in members])
+        self.assertLess(took, 1.0)
+
+
 if __name__ == '__main__':
     unittest.main()