SHA256 optimized for ComputerCraft

--
--  Adaptation of the Secure Hashing Algorithm (SHA-244/256)
--  Found Here: http://lua-users.org/wiki/SecureHashAlgorithm
--
--  Using an adapted version of the bit library
--  Found Here: https://bitbucket.org/Boolsheet/bslf/src/1ee664885805/bit.lua
--
--  API-d by randomdude999
--
local MOD=2^32
local MODM=MOD-1
local function memoize(f)
    local mt={}
    local t=setmetatable({}, mt)
    function mt:__index(k)
        local v=f(k)
        t[k]=v
        return v
    end
    return t
end
local function make_bitop_uncached(t,m)
    local function bitop(a,b)
        local res,p=0,1
        while a~=0 and b~=0 do
            local am,bm=a%m,b%m
            res=res+t[am][bm]*p
            a=(a-am)/m
            b=(b-bm)/m
            p=p*m
        end
        res=res+(a+b)*p
        return res
    end
    return bitop
end
local function make_bitop(t)
    local op1=make_bitop_uncached(t,2^1)
    local op2=memoize(function(a) return memoize(function(b) return op1(a,b) end) end)
    return make_bitop_uncached(op2,2^(t.n or 1))
end
local bxor1 = make_bitop({[0]={[0]=0,[1]=1},[1]={[0]=1,[1]=0},n=4})
local function bxor(a,b,c,...)
    local z=nil
    if b then
        a=a%MOD
        b=b%MOD
        z=bxor1(a,b)
        if c then z=bxor(z,c,...) end
        return z
    elseif a then return a%MOD
    else return 0 end
end
local function band(a,b,c,...)
    local z
    if b then
        a=a%MOD
        b=b%MOD
        z=((a+b)-bxor1(a,b))/2
        if c then z=bit32_band(z,c,...) end
        return z
    elseif a then return a%MOD
    else return MODM end
end
local function bnot(x) return (-1-x)%MOD end
local function rshift1(a,disp)
    if disp<0 then return lshift(a,-disp) end
    return math.floor(a%MOD/2^disp)
end
local function rshift(x,disp)
    if disp>31 or disp<-31 then return 0 end
    return rshift1(x%MOD,disp)
end
local function lshift(a,disp)
    if disp<0 then return rshift(a,-disp) end
    return (a*2^disp)%MOD
end
local function rrotate(x,disp)
    x=x%MOD
    disp=disp%32
    local low=band(x,2^disp-1)
    return rshift(x,disp)+lshift(low,32-disp)
end
local k = {
    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,
}
local function str2hexa(s)
    return (string.gsub(s,".",function(c) return string.format("%02x",string.byte(c)) end))
end
local function num2s(l,n)
    local s=""
    for i=1,n do
        local rem=l%256
        s=string.char(rem)..s
        l=(l-rem)/256
    end
    return s
end
local function s232num(s,i)
    local n=0
    for i=i,i+3 do n=n*256+string.byte(s,i) end
    return n
end
local function preproc(a, b)
    local c=64-((b+9)%64)
    b=num2s(8*b,8)
    a=a.."\128"..string.rep("\0",c)..b
    assert(#a%64==0)
    return a
end
local function digestblock(msg,i,H)
    local w={}
    for j=1,16 do w[j]=s232num(msg,i+(j-1)*4) end
    for j=17,64 do
        local v=w[j-15]
        local s0=bxor(rrotate(v,7),rrotate(v,18),rshift(v,3))
        v=w[j-2]
        w[j]=w[j-16]+s0+w[j-7]+bxor(rrotate(v,17),rrotate(v,19),rshift(v,10))
    end
    local a,b,c,d,e,f,g,h=H[1],H[2],H[3],H[4],H[5],H[6],H[7],H[8]
    for i=1,64 do
        local s0=bxor(rrotate(a,2),rrotate(a,13),rrotate(a,22))
        local maj=bxor(band(a,b),band(a,c), band(b,c))
        local t2=s0+maj
        local s1=bxor(rrotate(e,6),rrotate(e,11),rrotate(e,25))
        local ch=bxor(band(e,f),band(bnot(e),g))
        local t1=h+s1+ch+k[i]+w[i]
        h,g,f,e,d,c,b,a=g,f,e,d+t1,c,b,a,t1+t2
    end
    H[1]=band(H[1]+a)
    H[2]=band(H[2]+b)
    H[3]=band(H[3]+c)
    H[4]=band(H[4]+d)
    H[5]=band(H[5]+e)
    H[6]=band(H[6]+f)
    H[7]=band(H[7]+g)
    H[8]=band(H[8]+h)
end
function sha256(a)
    a = preproc(a, #a)
    local H = {0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19}
    for i = 1, #a, 64 do digestblock(a, i, H) end
    return str2hexa(num2s(H[1],4)..num2s(H[2],4)..num2s(H[3],4)..num2s(H[4],4)..num2s(H[5],4)..num2s(H[6],4)..num2s(H[7],4)..num2s(H[8],4))
end