From e6f0bcde3690ceac09f80ba50d4962d53b0c45f8 Mon Sep 17 00:00:00 2001
From: Franz Haas <franz.dominik.haas@gmail.com>
Date: Fri, 4 Oct 2024 22:08:17 +0200
Subject: [PATCH] - added capability to compile VarInt

---
 construct/core.py | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/construct/core.py b/construct/core.py
index 8f5919f0..57a52928 100644
--- a/construct/core.py
+++ b/construct/core.py
@@ -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):