Add a Lua implementation for MD5 checksum calculation

This script computes the MD5 checksum for files using Lua. It includes core MD5 transformations, padding, and file processing logic. The implementation also displays the checksum along with the file name or provides error handling for invalid inputs. The output mimics GNU coreutils version of `md5sum` being ran without any flags.

Author: Lethja

demo/extra/md5sum.lua

@@ -0,0 +1,152 @@
+#!/usr/bin/env lua
+
+local T = {} -- Predefined MD5 constants of sine-based shifts (T values)
+for i = 1, 64 do
+	T[i] = math.floor(2 ^ 32 * math.abs(math.sin(i)))
+end
+
+--- Read a files hash from it's current point to the end
+--- @param file file The file to read to the end
+--- @return string The md5 checksum result of the file
+function md5_file(file)
+	local function Md5Transform(chunk, A, B, C, D) -- Core MD5 transformation
+		local F = function(x, y, z)
+			return (x & y) | (~x & z)
+		end
+
+		local G = function(x, y, z)
+			return (x & z) | (y & ~z)
+		end
+
+		local H = function(x, y, z)
+			return x ~ y ~ z
+		end
+
+		local I = function(x, y, z)
+			return y ~ (x | ~z)
+		end
+
+		local function LShift32(x, n)
+			return ((x << n) | (x >> (32 - n))) & 0xFFFFFFFF
+		end
+
+		local words, shifts = {}, { { 7, 12, 17, 22 },
+						 { 5, 9, 14, 20 },
+						 { 4, 11, 16, 23 },
+						 { 6, 10, 15, 21 }
+		}
+
+		for i = 0, 15 do -- Break the chunk into 16 little-endian 32-bit words
+			local offset = i * 4 + 1
+			words[i + 1] = string.byte(chunk, offset) |
+					(string.byte(chunk, offset + 1) << 8) |
+					(string.byte(chunk, offset + 2) << 16) |
+					(string.byte(chunk, offset + 3) << 24)
+		end
+
+		local a, b, c, d = A, B, C, D
+
+		for i = 1, 64 do -- Main loop: 64 rounds of transformations
+			local f, g
+			local round = math.floor((i - 1) / 16) + 1
+			local shift = shifts[round][(i - 1) % 4 + 1]
+
+			if round == 1 then
+				f = F(b, c, d)
+				g = (i - 1) % 16
+			elseif round == 2 then
+				f = G(b, c, d)
+				g = (5 * (i - 1) + 1) % 16
+			elseif round == 3 then
+				f = H(b, c, d)
+				g = (3 * (i - 1) + 5) % 16
+			elseif round == 4 then
+				f = I(b, c, d)
+				g = (7 * (i - 1)) % 16
+			end
+
+			local temp = d
+			d = c
+			c = b
+			b = (b + LShift32((a + f + words[g + 1] +
+					T[i]) & 0xFFFFFFFF, shift)) & 0xFFFFFFFF
+			a = temp
+		end
+
+		-- Add chunk's hash to the result so far
+		A = (A + a) & 0xFFFFFFFF
+		B = (B + b) & 0xFFFFFFFF
+		C = (C + c) & 0xFFFFFFFF
+		D = (D + d) & 0xFFFFFFFF
+
+		return A, B, C, D
+	end
+
+	local function Md5Pad(messageLength)
+		local msg_len = messageLength * 8 -- Message length in bits
+		local padding = "\128" -- Initial padding
+		local pad_len = (56 - (messageLength % 64)) -- 448 mod 512
+
+		if pad_len <= 0 then
+			pad_len = pad_len + 64
+		end
+
+		padding = padding .. string.rep("\0", pad_len - 1)
+
+		-- Append the original message length as a 64-bit little-endian integer
+		for i = 0, 7 do
+			padding = padding .. string.char((msg_len >> (8 * i)) & 0xFF)
+		end
+
+		return padding
+	end
+
+    local A, B, C, D, len = 0x67452301, 0xefcdab89, 0x98badcfe, 0x10325476, 0
+
+    while true do
+        local chunk = file:read(64) -- Read in chunks of 64 bytes (512 bits)
+
+        if not chunk then break end
+        len = len + #chunk
+
+		-- If it's the final chunk, apply padding
+        if #chunk < 64 then chunk = chunk .. Md5Pad(len) end
+        A, B, C, D = Md5Transform(chunk, A, B, C, D)
+
+		-- Stop processing after the padded block
+        if #chunk > 64 then break end
+    end
+
+	-- Format output as a hexadecimal string in little-endian order
+    local function to_hex(x)
+        return string.format("%02x%02x%02x%02x",
+				x & 0xFF, (x >> 8) & 0xFF, (x >> 16) & 0xFF, (x >> 24) & 0xFF)
+    end
+
+    return to_hex(A) .. to_hex(B) .. to_hex(C) .. to_hex(D)
+end
+
+if #arg < 1 then
+	-- Show accurate Lua binary and script location
+    print((arg[-1] or "?") .. " " .. (arg[0] or "?") .. " [FILE]...")
+    os.exit(1)
+else
+    for i = 1, #arg do
+        local file, err = io.open(arg[i], "rb")
+
+        if file then
+            local sum = md5_file(file)
+            file:close()
+
+            if sum then
+                print(sum .. "  " .. arg[i])
+            else
+                print(arg[i] .. ": " .. "Unknown error")
+                os.exit(-1)
+            end
+        else
+            print(arg[i] .. ": " .. err)
+            os.exit(1)
+        end
+    end
+end