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diff --git a/standalone/encode.py b/standalone/encode.py
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+++ b/standalone/encode.py
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+# Copyright 2018 The gemmlowp Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Encodes ARM asm code for certain instructions into the corresponding machine code encoding, as a .word directive in the asm code, preserving the original code in a comment.
+
+Reads from stdin, writes to stdout.
+
+Example diff:
+-        "udot v16.4s, v4.16b, v0.16b\n"
++        ".word 0x6e809490  // udot v16.4s, v4.16b, v0.16b\n"
+
+The intended use case is to make asm code easier to compile on toolchains that
+do not support certain new instructions.
+"""
+
+import sys
+import re
+import argparse
+
+
+def encode_udot_sdot_vector(line):
+  m = re.search(
+      r'\b([us])dot[ ]+v([0-9]+)[ ]*\.[ ]*4s[ ]*\,[ ]*v([0-9]+)[ ]*\.[ ]*16b[ ]*\,[ ]*v([0-9]+)[ ]*\.[ ]*16b',
+      line)
+  if not m:
+    return 0, line
+
+  match = m.group(0)
+  unsigned = 1 if m.group(1) == 'u' else 0
+  accum = int(m.group(2))
+  lhs = int(m.group(3))
+  rhs = int(m.group(4))
+  assert accum >= 0 and accum <= 31
+  assert lhs >= 0 and lhs <= 31
+  assert rhs >= 0 and rhs <= 31
+  mcode = 0x4e809400 | (accum << 0) | (lhs << 5) | (rhs << 16) | (
+      unsigned << 29)
+  return mcode, match
+
+
+def encode_udot_sdot_element(line):
+  m = re.search(
+      r'\b([us])dot[ ]+v([0-9]+)[ ]*\.[ ]*4s[ ]*\,[ ]*v([0-9]+)[ ]*\.[ ]*16b[ ]*\,[ ]*v([0-9]+)[ ]*\.[ ]*4b[ ]*\[([0-9])\]',
+      line)
+  if not m:
+    return 0, line
+
+  match = m.group(0)
+  unsigned = 1 if m.group(1) == 'u' else 0
+  accum = int(m.group(2))
+  lhs = int(m.group(3))
+  rhs = int(m.group(4))
+  lanegroup = int(m.group(5))
+  assert accum >= 0 and accum <= 31
+  assert lhs >= 0 and lhs <= 31
+  assert rhs >= 0 and rhs <= 31
+  assert lanegroup >= 0 and lanegroup <= 3
+  l = 1 if lanegroup & 1 else 0
+  h = 1 if lanegroup & 2 else 0
+  mcode = 0x4f80e000 | (accum << 0) | (lhs << 5) | (rhs << 16) | (l << 21) | (
+      h << 11) | (
+          unsigned << 29)
+  return mcode, match
+
+
+def encode(line):
+  for encode_func in [encode_udot_sdot_vector, encode_udot_sdot_element]:
+    mcode, match = encode_func(line)
+    if mcode:
+      return mcode, match
+  return 0, line
+
+
+def read_existing_encoding(line):
+  m = re.search(r'\.word\ (0x[0-9a-f]+)', line)
+  if m:
+    return int(m.group(1), 16)
+  return 0
+
+
+parser = argparse.ArgumentParser(description='Encode some A64 instructions.')
+parser.add_argument(
+    '-f',
+    '--fix',
+    help='fix existing wrong encodings in-place and continue',
+    action='store_true')
+args = parser.parse_args()
+
+lineno = 0
+found_existing_encodings = False
+found_error = False
+found_fixes = False
+for line in sys.stdin:
+  lineno = lineno + 1
+  mcode, match = encode(line)
+  if mcode:
+    existing_encoding = read_existing_encoding(line)
+    if existing_encoding:
+      found_existing_encodings = True
+      if mcode != existing_encoding:
+        if args.fix:
+          line = line.replace('.word 0x%x  // %s' % (existing_encoding, match),
+                              '.word 0x%x  // %s' % (mcode, match))
+          found_fixes = True
+        else:
+          sys.stderr.write(
+              "Error at line %d: existing encoding 0x%x differs from encoding 0x%x for instruction '%s':\n\n%s\n\n"
+              % (lineno, existing_encoding, mcode, match, line))
+          found_error = True
+    else:
+      line = line.replace(match, '.word 0x%x  // %s' % (mcode, match))
+  sys.stdout.write(line)
+if found_error:
+  sys.exit(1)
+if found_existing_encodings:
+  if found_fixes:
+    sys.stderr.write(
+        'Note: some instructions that this program is able to encode, were already encoded and their existing encodings didn\'t match the specified asm instructions. Since --fix was passed, these were fixed in-place.\n'
+    )
+  else:
+    sys.stderr.write(
+        'Note: some instructions that this program is able to encode, were already encoded. These encodings have been checked.\n'
+    )