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- added capability to compile VarInt #1097

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33 changes: 33 additions & 0 deletions construct/core.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1646,6 +1646,39 @@ def _build(self, obj, stream, context, path):
def _emitprimitivetype(self, ksy, bitwise):
return "vlq_base128_le"

def _emitparse(self, code):
code.append("""
def parse_varint(io):
acc = []
while True:
b = byte2int(io.read(1))
acc.append(b & 0b01111111)
if b & 0b10000000 == 0:
break
num = 0
for b in reversed(acc):
num = (num << 7) | b
return num
""")
return "parse_varint(io)"

def _emitbuild(self, code):
code.append("""
def build_varint(io, obj):
if not isinstance(obj, int):
raise IntegerError(f"value {obj} is not an integer", path=path)
if obj < 0:
raise IntegerError(f"VarInt cannot build from negative number {obj}", path=path)
x = obj
B = bytearray()
while x > 0b01111111:
B.append(0b10000000 | (x & 0b01111111))
x >>= 7
B.append(x)
io.write(bytes(B))
return obj
""")
return "build_varint(io, obj)"

@singleton
class ZigZag(Construct):
Expand Down