Simplify bn2vch using int.to_bytes

Author: sipa

test/functional/test_framework/script.py

@@ -27,38 +27,14 @@ def hash160(s):
 
 def bn2vch(v):
     """Convert number to bitcoin-specific little endian format."""
-    # The top bit is used to indicate the sign of the number. If there
-    # isn't a spare bit in the bit length, add an extension byte.
-    have_ext = False
-    ext = bytearray()
-    if v.bit_length() > 0:
-        have_ext = (v.bit_length() & 0x07) == 0
-        ext.append(0)
-
-    # Is the number negative?
-    neg = False
-    if v < 0:
-        neg = True
-        v = -v
-
-    # Convert the int to bytes
-    v_bin = bytearray()
-    bytes_len = (v.bit_length() + 7) // 8
-    for i in range(bytes_len, 0, -1):
-        v_bin.append((v >> ((i - 1) * 8)) & 0xff)
-
-    # Add the sign bit if necessary
-    if neg:
-        if have_ext:
-            ext[0] |= 0x80
-        else:
-            v_bin[0] |= 0x80
-
-    v_bytes = ext + v_bin
-    # Reverse bytes ordering for LE
-    v_bytes.reverse()
-
-    return bytes(v_bytes)
+    # We need v.bit_length() bits, plus a sign bit for every nonzero number.
+    n_bits = v.bit_length() + (v != 0)
+    # The number of bytes for that is:
+    n_bytes = (n_bits + 7) // 8
+    # Convert number to absolute value + sign in top bit.
+    encoded_v = 0 if v == 0 else abs(v) | ((v < 0) << (n_bytes * 8 - 1))
+    # Serialize to bytes
+    return encoded_v.to_bytes(n_bytes, 'little')
 
 _opcode_instances = []
 class CScriptOp(int):