src/Pure/General/sha1.ML

improved treatment of Element.Obtains via Expression.prepare_stmt;
discontinued pointless all_types ctxt: prep_var is always sequential;

(*  Title:      Pure/General/sha1.ML
    Author:     Makarius

Digesting strings according to SHA-1 (see RFC 3174) -- relatively slow
version in pure ML.
*)

signature SHA1 =
sig
  eqtype digest
  val digest: string -> digest
  val rep: digest -> string
  val fake: string -> digest
end;

structure SHA1: SHA1 =
struct

(* 32bit words *)

infix 4 << >>;
infix 3 andb;
infix 2 orb xorb;

val op << = Word32.<<;
val op >> = Word32.>>;
val op andb = Word32.andb;
val op orb = Word32.orb;
val op xorb = Word32.xorb;
val notb = Word32.notb;

fun rotate k w = w << k orb w >> (0w32 - k);


(* hexadecimal words *)

fun hex_digit (text, w: Word32.word) =
  let
    val d = Word32.toInt (w andb 0wxf);
    val dig = if d < 10 then chr (ord "0" + d) else chr (ord "a" + d - 10);
  in (dig ^ text, w >> 0w4) end;

fun hex_word w = #1 (funpow 8 hex_digit ("", w));


(* padding *)

fun pack_bytes 0 n = ""
  | pack_bytes k n = pack_bytes (k - 1) (n div 256) ^ chr (n mod 256);

fun padded_text str =
  let
    val len = size str;
    val padding = chr 128 ^ replicate_string (~ (len + 9) mod 64) (chr 0) ^ pack_bytes 8 (len * 8);
    fun byte i = Char.ord (String.sub (if i < len then (str, i) else (padding, (i - len))));
    fun word i =
      Word32.fromInt (byte (4 * i)) << 0w24 orb
      Word32.fromInt (byte (4 * i + 1)) << 0w16 orb
      Word32.fromInt (byte (4 * i + 2)) << 0w8 orb
      Word32.fromInt (byte (4 * i + 3));
  in ((len + size padding) div 4, word) end;


(* digest_string *)

fun digest_word (i, w, {a, b, c, d, e}) =
  let
    val {f, k} =
      if i < 20 then
        {f = (b andb c) orb (notb b andb d),
         k = 0wx5A827999}
      else if i < 40 then
        {f = b xorb c xorb d,
         k = 0wx6ED9EBA1}
      else if i < 60 then
        {f = (b andb c) orb (b andb d) orb (c andb d),
         k = 0wx8F1BBCDC}
      else
        {f = b xorb c xorb d,
         k = 0wxCA62C1D6};
    val op + = Word32.+;
  in
    {a = rotate 0w5 a + f + e + w + k,
     b = a,
     c = rotate 0w30 b,
     d = c,
     e = d}
  end;

fun digest_string str =
  let
    val (text_len, text) = padded_text str;

    (*hash result -- 5 words*)
    val hash_array : Word32.word Array.array =
      Array.fromList [0wx67452301, 0wxEFCDAB89, 0wx98BADCFE, 0wx10325476, 0wxC3D2E1F0];
    fun hash i = Array.sub (hash_array, i);
    fun add_hash x i = Array.update (hash_array, i, hash i + x);

    (*current chunk -- 80 words*)
    val chunk_array = Array.array (80, 0w0: Word32.word);
    fun chunk i = Array.sub (chunk_array, i);
    fun init_chunk pos =
      Array.modifyi (fn (i, _) =>
        if i < 16 then text (pos + i)
        else rotate 0w1 (chunk (i - 3) xorb chunk (i - 8) xorb chunk (i - 14) xorb chunk (i - 16)))
      chunk_array;

    fun digest_chunks pos =
      if pos < text_len then
        let
          val _ = init_chunk pos;
          val {a, b, c, d, e} = Array.foldli digest_word
            {a = hash 0,
             b = hash 1,
             c = hash 2,
             d = hash 3,
             e = hash 4}
            chunk_array;
          val _ = add_hash a 0;
          val _ = add_hash b 1;
          val _ = add_hash c 2;
          val _ = add_hash d 3;
          val _ = add_hash e 4;
        in digest_chunks (pos + 16) end
      else ();
    val _  = digest_chunks 0;

    val hex = hex_word o hash;
  in hex 0 ^ hex 1 ^ hex 2 ^ hex 3 ^ hex 4 end;


(* type digest *)

datatype digest = Digest of string;

val digest = Digest o digest_string;
fun rep (Digest s) = s;

val fake = Digest;

end;