From c6a1f7372d19418004c2c86403c90ff88a6c77c4 Mon Sep 17 00:00:00 2001
From: John Brophy <john_brophys@waters.com>
Date: Thu, 31 May 2018 15:56:22 +0100
Subject: [PATCH] fix issue #38 - decode negative int32

---
 pb/standard/unpack.lua        | 19 +++++++++++++++++++
 protos/int32.proto            |  4 ++++
 tests/test_negative_int32.lua | 13 +++++++++++++
 3 files changed, 36 insertions(+)
 create mode 100644 protos/int32.proto
 create mode 100644 tests/test_negative_int32.lua

diff --git a/pb/standard/unpack.lua b/pb/standard/unpack.lua
index 9f5840e..6b80446 100644
--- a/pb/standard/unpack.lua
+++ b/pb/standard/unpack.lua
@@ -116,10 +116,26 @@ local function unpack_varint64(data, off, max_off, signed)
 	return num, off + 1
 end
 
+local function unpack_neg_varint32(data, off, max_off)
+	local boff = 1
+	local num = 0
+	local bits35 = 34359738368 -- 2^(5*7)
+	for i = 1, 5 do
+		num = num + (band(data:byte(off), 0x7F) * boff)
+		off = off + 1
+		boff = boff * 128
+	end
+	while data:byte(off) >= 128 do
+		off = off + 1
+  end
+	return num - bits35, off + 1
+end
+
 local function unpack_varint32(data, off, max_off)
 	local b = data:byte(off)
 	local num = band(b, 0x7F)
 	local boff = 128
+  local start_off = off
 	while b >= 128 do
 		off = off + 1
 		if off > max_off then
@@ -129,6 +145,9 @@ local function unpack_varint32(data, off, max_off)
 		num = num + (band(b, 0x7F) * boff)
 		boff = boff * 128
 	end
+	if off - start_off + 1 == 10 then
+		return unpack_neg_varint32(data, start_off, max_off)
+	end
 	return num, off + 1
 end
 
diff --git a/protos/int32.proto b/protos/int32.proto
new file mode 100644
index 0000000..4897f07
--- /dev/null
+++ b/protos/int32.proto
@@ -0,0 +1,4 @@
+message TestInt32
+{
+    optional int32 int32_ = 1;
+}
\ No newline at end of file
diff --git a/tests/test_negative_int32.lua b/tests/test_negative_int32.lua
new file mode 100644
index 0000000..fc116f7
--- /dev/null
+++ b/tests/test_negative_int32.lua
@@ -0,0 +1,13 @@
+local pb = require"pb"
+local value = -1
+local integer32 = require"protos.int32"
+
+local msg = integer32.TestInt32()
+msg.int32_ = value;
+binary,err = msg:Serialize();
+assert(not err)
+
+local decoded = integer32.TestInt32():Parse(binary)
+assert(decoded:IsInitialized())
+assert(decoded:HasField('int32_'))
+assert(value == decoded.int32_)
\ No newline at end of file