--- a/hglib.lua	Thu Sep 08 19:40:38 2016 +0800
+++ b/hglib.lua	Thu Sep 08 20:46:39 2016 +0800
@@ -25,6 +25,18 @@
 	end
 end
 
+local function decode_i4(bytestring)
+	local value = 0
+	for i = 1, sizes.i4 do
+		local byte = bytestring:sub(i, i):byte()
+		value = value + byte * (2 ^ ((sizes.i4 - i) * 8))
+	end
+	if value >= 2 ^ (sizes.i4 * 8 - 1) then
+		value = value - 2 ^ (sizes.i4 * 8)
+	end
+	return value
+end
+
 local Client = {}
 Client.__index = Client
 
@@ -103,5 +115,6 @@
 	read_u4 = read_u4,
 	read_c = read_c,
 	read_channel = read_channel,
+	decode_i4 = decode_i4,
 	Client = Client
 }

--- a/spec/hglib_spec.lua	Thu Sep 08 19:40:38 2016 +0800
+++ b/spec/hglib_spec.lua	Thu Sep 08 20:46:39 2016 +0800
@@ -1,5 +1,22 @@
 local hglib = require('hglib')
 
+describe('hglib helper functions', function()
+	describe('decode_i4', function()
+		it('can decode 0', function()
+			assert.are_equal(0, hglib.decode_i4('\0\0\0\0'))
+		end)
+		it('can decode 255', function()
+			assert.are_equal(255, hglib.decode_i4('\0\0\0\255'))
+		end)
+		it('can decode 256', function()
+			assert.are_equal(256, hglib.decode_i4('\0\0\1\0'))
+		end)
+		it('can decode -1', function()
+			assert.are_equal(-1, hglib.decode_i4('\255\255\255\255'))
+		end)
+	end)
+end)
+
 describe('hglib client', function()
 	it('can connect using just file handles', function()
 		local rh = io.open('spec/data/hello', 'rb')