1		% (c) 2009-2013 Lehrstuhl fuer Softwaretechnik und Programmiersprachen,
2		% Heinrich Heine Universitaet Duesseldorf
3		% This software is licenced under EPL 1.0 (http://www.eclipse.org/org/documents/epl-v10.html)
4
5		:- module(probhash, [add_term/3, reset_probhash/0, hash_term/2, hash_to_atom/2, raw_sha_hash/2]).
6		:- use_module(library(fastrw),[ fast_buf_read/2,
7		fast_buf_write/3 ]).
8
9		:- use_module('../../src/module_information.pl').
10
11		:- module_info(group,infrastructure).
12		:- module_info(description,'This is the interface to C code for generating good hashes (SHA-1).').
13
14		foreign_resource(probhash,[sha1]).
15		foreign(sha1,sha1(+address(char),+integer,[-term])).
16
17		:- dynamic is_initialised/0.
18
19		init_probhash :- is_initialised,!.
20		init_probhash :-
21		load_foreign_resource(library(probhash)),
22		assert(is_initialised).
23
24		% input: term
25		% output: hash value as a biginteger (the byte order is reversed)
26		hash_term(Term,Hash) :- raw_sha_hash(Term,H), hash_to_int(H,Hash).
27
28		:- dynamic hash_id/1.
29		:- dynamic hash_h1h2/2.
30		:- dynamic hash_h2h3/2.
31		:- dynamic hash_h3h4/2.
32		:- dynamic hash_h4h5/2.
33		:- dynamic hash_h5id/2.
34
35		reset_probhash :-
36		retractall(hash_id(_)), assert(hash_id(0)),
37		retractall(hash_h1h2(_,_)), retractall(hash_h2h3(_,_)),
38		retractall(hash_h3h4(_,_)), retractall(hash_h4h5(_,_)),
39		retractall(hash_h5id(_,_)).
40
41		hash_id(0).
42
43		gen_new_id(X) :- hash_id(N), retract(hash_id(N)), X is N + 1, assert(hash_id(X)).
44
45		lookup(H1,H2,H3,H4,H5,X) :-
46		hash_h1h2(H1,H2), hash_h2h3(H2,H3), hash_h3h4(H3,H4), hash_h4h5(H4,H5), hash_h5id(H5,X).
47
48		store_hash(H1,H2,H3,H4,H5,X) :-
49		assert_hash_h1h2(H1,H2), assert_hash_h2h3(H2,H3), assert_hash_h3h4(H3,H4),
50		assert_hash_h4h5(H4,H5), assert(hash_h5id(H5,X)).
51
52		assert_hash_h1h2(X,Y) :- hash_h1h2(X,Y) -> true ; assert(hash_h1h2(X,Y)).
53		assert_hash_h2h3(X,Y) :- hash_h2h3(X,Y) -> true ; assert(hash_h2h3(X,Y)).
54		assert_hash_h3h4(X,Y) :- hash_h3h4(X,Y) -> true ; assert(hash_h3h4(X,Y)).
55		assert_hash_h4h5(X,Y) :- hash_h4h5(X,Y) -> true ; assert(hash_h4h5(X,Y)).
56
57		add_term(Term, Id, New) :- raw_sha_hash(Term,TH), hash_to_32bit(TH,[H1,H2,H3,H4,H5]),
58		( lookup(H1,H2,H3,H4,H5,X) ->
59		New=false, Id=X
60		; otherwise ->
61		New = true, gen_new_id(Id), store_hash(H1,H2,H3,H4,H5,Id)).
62
63
64		% input: raw hash
65		% output: hash value as a biginteger (the byte order is reversed)
66		hash_to_int(X,Y) :- hash_to_int(X,0,Y).
67		hash_to_int([],A,A).
68		hash_to_int([H|T],A,R) :- A2 is A * 256 + H, hash_to_int(T,A2,R).
69
70		% raw sha hashing, input is a term, output a raw hash, i.e., a list of 20 bytes
71		raw_sha_hash(Term,Digest) :-
72		init_probhash,
73		fast_buf_write(Term,Len,Addr),
74		sha1(Addr,Len,Digest).
75
76		% input: raw hash value
77		% output: hash value as an atom
78		hash_to_atom(H,ResultAtom) :-
79		raw_sha_hash(H,H2), hash_to_int(H2,X),
80		number_codes(X, C),atom_codes(ResultAtom,C).
81
82		% input: raw hash value
83		% output: hash value as 5 32-bit chunks
84		hash_to_32bit([V1,V2,V3,V4,V5,V6,V7,V8,V9,V10,V11,V12,V13,V14,V15,V16,V17,V18,V19,V20],[H1,H2,H3,H4,H5]) :-
85		hash_to_int([V1,V2,V3,V4],H1),
86		hash_to_int([V5,V6,V7,V8],H2),
87		hash_to_int([V9,V10,V11,V12],H3),
88		hash_to_int([V13,V14,V15,V16],H4),
89		hash_to_int([V17,V18,V19,V20],H5).