S256SUM.LUA

#!/usr/bin/env lua

---Get file hash
---@param file file The file
---@return string SHA-256 checksum
function sha256_file(file)

	-- M = Maximum value of number (32-bits)
	-- K = SHA256 round constants
	local M, K = 0xFFFFFFFF, {
		0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
		0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
		0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
		0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
		0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
		0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
		0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
		0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
		0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
		0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
		0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
	}

	---Right rotate a 32-bit value
	---@param x number The 32-bit value to be rotated
	---@param n number The number of rotations to the right that should be done
	---@return number The right shifted value
	local function RR(x, n)
		return (x >> n) | ((x & M) << (32 - n))
	end

	---SHA-256 transformation function
	---@param k string A 64-byte chunk of the message
	---@param H table The current hash state (8 32-bit values)
	local function TF(k, H)

		-- W = list of 32-bit words
		local W = {}

		for i = 0, 15 do -- Convert chunk into 32-bit list

			-- o = Offset calculation
			local o = i * 4 + 1

			W[i] = string.byte(k, o) << 24 | string.byte(k, o + 1) << 16 | string.byte(k, o + 2) << 8 | string.byte(k, o + 3)
		end

		for i = 16, 63 do -- Message expansion

			-- s0 = Message schedule shift 0
			-- s1 = Message schedule shift 1
			local s0, s1 = RR(W[i - 15], 7) ~ RR(W[i - 15], 18) ~ (W[i - 15] >> 3), RR(W[i - 2], 17) ~ RR(W[i - 2], 19) ~ (W[i - 2] >> 10)

			W[i] = (W[i - 16] + s0 + W[i - 7] + s1) & M
		end

		-- 32-bit working variables initialized with the current hash values of H
		local a, b, c, d, e, f, g, h = table.unpack(H)

		for i = 0, 63 do

			-- S0 = Compression rotation variable 0
			-- S1 = Compression rotation variable 1
			-- ch = Choice function
			-- ma = Majority function
			local S0, S1, ch, ma = RR(a, 2) ~ RR(a, 13) ~ RR(a, 22), RR(e, 6) ~ RR(e, 11) ~ RR(e, 25), (e & f) ~ ((~e) & g), (a & b) ~ (a & c) ~ (b & c)

			-- t1 = Temporary variable 1
			-- t2 = Temporary variable 2
			local t1, t2 = (h + S1 + ch + K[i + 1] + W[i]) & M, (S0 + ma) & M

			-- Working variable update
			h = g
			g = f
			f = e
			e = (d + t1) & M
			d = c
			c = b
			b = a
			a = (t1 + t2) & M
		end

		-- Update hash state with compressed block values
		H[1] = (H[1] + a) & M
		H[2] = (H[2] + b) & M
		H[3] = (H[3] + c) & M
		H[4] = (H[4] + d) & M
		H[5] = (H[5] + e) & M
		H[6] = (H[6] + f) & M
		H[7] = (H[7] + g) & M
		H[8] = (H[8] + h) & M
	end

	---Create SHA-256 padding for message
	---@param l number The length of the message in bytes
	---@return string The padding string to append to the message
	local function P(l)

		-- ml = Message length (in bits)
		--  p = Padding string
		-- pl = Padding length (in bytes)
		local ml, p, pl = l * 8, "\128", 56 - (l % 64)

		-- Add enough room for padding if required
		if pl <= 0 then
			pl = pl + 64
		end

		-- Zero out padding
		p = p .. string.rep("\0", pl - 1)

		-- Append original message length
		for i = 7, 0, -1 do
			p = p .. string.char((ml >> (i * 8)) & 0xFF)
		end

		return p
	end

	-- H = Initial Hash values
	-- l = Total bytes of file processed
	local H, l = { 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 }, 0

	while 1 do

		-- c = 64 byte chunk of file
		local c = file:read(64)

		if not c then
			break
		end

		l = l + #c

		if #c < 64 then
			c = c .. P(l)
			TF(c, H)
			break
		end

		TF(c, H)
	end

	-- l = Final hash string
	l = ""

	for _, v in ipairs(H) do
		l = l .. string.format("%08x", v)
	end

	return l
end

if LIB then
	return -- Don't run below code if brought in as a library
end

if #arg < 1 then -- Print help and exit if no arguments
	print((arg[-1] or "?") .. " " .. (arg[0] or "?") .. " [FILE]...")
	os.exit(1)
else
	for i = 1, #arg do

		-- f = File to read
		-- e = Error message on failure to open
		local f, e = io.open(arg[i], "rb")

		if not f then
			print(e)
			os.exit(1)
		end

		-- s = SHA256 string of file
		local s = sha256_file(f)

		f:close()

		if s then -- Print hash and filename
			print(s .. "  " .. arg[i])
		else
			print(arg[i] .. ": " .. "Unknown error")
			os.exit(-1)
		end
	end
end