Datasets:

Modalities:
Text
Languages:
English
Libraries:
Datasets
License:
File size: 7,240 Bytes
4365a98
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
(* ========================================================================= *)
(* Definition of "bitsize", how many bits are needed for a natural number.   *)
(* ========================================================================= *)

let bitsize = new_definition
 `bitsize n = minimal i. n < 2 EXP i`;;

let BITSIZE_0 = prove
 (`bitsize 0 = 0`,
  REWRITE_TAC[bitsize] THEN MATCH_MP_TAC MINIMAL_UNIQUE THEN ARITH_TAC);;

let BITSIZE_POW2 = prove
 (`!k. bitsize (2 EXP k) = k + 1`,
  GEN_TAC THEN REWRITE_TAC[bitsize; LT_EXP] THEN
  MATCH_MP_TAC MINIMAL_UNIQUE THEN ARITH_TAC);;

let BITSIZE_1 = prove
 (`bitsize 1 = 1`,
  MP_TAC(SPEC `0` BITSIZE_POW2) THEN CONV_TAC NUM_REDUCE_CONV);;

let BITSIZE_2 = prove
 (`bitsize 2 = 2`,
  MP_TAC(SPEC `1` BITSIZE_POW2) THEN CONV_TAC NUM_REDUCE_CONV);;

let BITSIZE_LE = prove
 (`!n k. bitsize n <= k <=> n < 2 EXP k`,
  REPEAT GEN_TAC THEN REWRITE_TAC[bitsize] THEN
  SIMP_TAC[MINIMAL_LE; MESON[LT_POW2_REFL] `?i. n < 2 EXP i`] THEN
  EQ_TAC THENL [ALL_TAC; MESON_TAC[LE_REFL]] THEN
  DISCH_THEN(X_CHOOSE_THEN `i:num` (CONJUNCTS_THEN2 ASSUME_TAC MP_TAC)) THEN
  MATCH_MP_TAC(REWRITE_RULE[IMP_CONJ_ALT] LTE_TRANS) THEN
  ASM_REWRITE_TAC[LE_EXP; ARITH_EQ]);;

let BITSIZE = prove
 (`!n. n < 2 EXP bitsize n`,
  REWRITE_TAC[GSYM BITSIZE_LE; LE_REFL]);;

let BITSIZE_UNIQUE = prove
 (`!n k. bitsize n = k <=> n < 2 EXP k /\ !j. j < k ==> 2 EXP j <= n`,
  REWRITE_TAC[GSYM NOT_LT; GSYM BITSIZE_LE] THEN
  MESON_TAC[LT_ANTISYM; LT_CASES; LT_TRANS]);;

let BITSIZE_UNIQUE_ALT = prove
 (`!n k. bitsize n = k <=> !j. n < 2 EXP j <=> k <= j`,
  REWRITE_TAC[BITSIZE_UNIQUE] THEN
  MESON_TAC[NOT_LE; LE_EXP; ARITH_RULE `~(2 = 0)`; LE_TRANS; LE_ANTISYM]);;

let BITSIZE_EQ_0 = prove
 (`!n. bitsize n = 0 <=> n = 0`,
  REWRITE_TAC[BITSIZE_UNIQUE; LT] THEN ARITH_TAC);;

let BITSIZE_MONO = prove
 (`!m n. m <= n ==> bitsize m <= bitsize n`,
  REPEAT STRIP_TAC THEN REWRITE_TAC[BITSIZE_LE] THEN
  TRANS_TAC LET_TRANS `n:num` THEN ASM_REWRITE_TAC[BITSIZE]);;

let BITSIZE_MAX = prove
 (`!m n. bitsize(MAX m n) = MAX (bitsize m) (bitsize n)`,
  REPEAT GEN_TAC THEN DISJ_CASES_TAC(ARITH_RULE `m:num <= n \/ n <= m`) THEN
  ASM_SIMP_TAC[ARITH_RULE `m <= n ==> MAX m n = n`; BITSIZE_MONO;
               ARITH_RULE `n <= m ==> MAX m n = m`]);;

let BITSIZE_MIN = prove
 (`!m n. bitsize(MIN m n) = MIN (bitsize m) (bitsize n)`,
  REPEAT GEN_TAC THEN DISJ_CASES_TAC(ARITH_RULE `m:num <= n \/ n <= m`) THEN
  ASM_SIMP_TAC[ARITH_RULE `m <= n ==> MIN m n = m`; BITSIZE_MONO;
               ARITH_RULE `n <= m ==> MIN m n = n`]);;

let BITSIZE_MULT_LE = prove
 (`!m n. bitsize(m * n) <= bitsize m + bitsize n`,
  REPEAT GEN_TAC THEN REWRITE_TAC[BITSIZE_LE; EXP_ADD] THEN
  MATCH_MP_TAC LT_MULT2 THEN REWRITE_TAC[BITSIZE]);;

let BITSIZE_REV_EQ = prove
 (`!n. 2 EXP (bitsize n - 1) <= n <=> ~(n = 0)`,
  REWRITE_TAC[GSYM NOT_LT; GSYM BITSIZE_LE] THEN
  REWRITE_TAC[ARITH_RULE `n - 1 < n <=> ~(n = 0)`; BITSIZE_EQ_0]);;

let BITSIZE_REV = prove
 (`!n. ~(n = 0) ==> 2 EXP (bitsize n - 1) <= n`,
  REWRITE_TAC[BITSIZE_REV_EQ]);;

let BITSIZE_REV_EQ_ALT = prove
 (`!n. 2 EXP (bitsize n) <= 2 * n <=> ~(n = 0)`,
  GEN_TAC THEN ASM_CASES_TAC `n = 0` THEN
  ASM_REWRITE_TAC[BITSIZE_0; ARITH] THEN
  TRANS_TAC LE_TRANS `2 * 2 EXP (bitsize n - 1)` THEN
  ASM_REWRITE_TAC[LE_MULT_LCANCEL; BITSIZE_REV_EQ] THEN
  REWRITE_TAC[GSYM(CONJUNCT2 EXP)] THEN
  MATCH_MP_TAC EQ_IMP_LE THEN AP_TERM_TAC THEN
  ASM_REWRITE_TAC[ARITH_RULE `n = SUC(n - 1) <=> ~(n = 0)`; BITSIZE_EQ_0]);;

let BITSIZE_REV_ALT = prove
 (`!n. ~(n = 0) ==> 2 EXP bitsize n <= 2 * n`,
  REWRITE_TAC[BITSIZE_REV_EQ_ALT]);;

let LE_BITSIZE = prove
 (`!n k. k <= bitsize n <=> ~(k = 0) ==> 2 EXP (k - 1) <= n`,
  REPEAT GEN_TAC THEN ASM_CASES_TAC `k = 0` THEN
  ASM_REWRITE_TAC[LE_0; ARITH] THEN
  REWRITE_TAC[GSYM NOT_LT; GSYM BITSIZE_LE] THEN ASM_ARITH_TAC);;

let LE_BITSIZE_ALT = prove
 (`!n k. k <= bitsize n <=> ~(k = 0) ==> 2 EXP k <= 2 * n`,
  REPEAT GEN_TAC THEN REWRITE_TAC[LE_BITSIZE] THEN
  ASM_CASES_TAC `k = 0` THEN ASM_REWRITE_TAC[] THEN
  MATCH_MP_TAC(ARITH_RULE `2 * a = b ==> (a <= n <=> b <= 2 * n)`) THEN
  REWRITE_TAC[GSYM(CONJUNCT2 EXP)] THEN AP_TERM_TAC THEN ASM_ARITH_TAC);;

let BITSIZE_UNIQUE_EQ = prove
 (`!n k. bitsize n = k <=>
         n < 2 EXP k /\ (~(k = 0) ==> 2 EXP k <= 2 * n)`,
  REPEAT GEN_TAC THEN GEN_REWRITE_TAC LAND_CONV
   [ARITH_RULE `n = k <=> k <= n /\ ~(k + 1 <= n)`] THEN
  REWRITE_TAC[LE_BITSIZE_ALT; EXP_ADD] THEN ARITH_TAC);;

let BITSIZE_MULT = prove
 (`(!k n. bitsize (2 EXP k * n) = if n = 0 then 0 else k + bitsize n) /\
   (!k n. bitsize (n * 2 EXP k) = if n = 0 then 0 else bitsize n + k)`,
  MATCH_MP_TAC(TAUT `(p ==> q) /\ p ==> p /\ q`) THEN CONJ_TAC THENL
   [REWRITE_TAC[MULT_SYM; ADD_SYM]; REPEAT GEN_TAC] THEN
  COND_CASES_TAC THEN ASM_REWRITE_TAC[MULT_CLAUSES; BITSIZE_0] THEN
  REWRITE_TAC[GSYM LE_ANTISYM; LE_BITSIZE_ALT; BITSIZE_LE] THEN
  ONCE_REWRITE_TAC[ARITH_RULE `2 * a * b = a * 2 * b`] THEN
  REWRITE_TAC[EXP_ADD; LT_MULT_LCANCEL; LE_MULT_LCANCEL] THEN
  ASM_REWRITE_TAC[BITSIZE; EXP_EQ_0; ARITH_EQ; BITSIZE_REV_EQ_ALT]);;

let BITSIZE_MULT_ADD = prove
 (`(!k m n. ~(m = 0) /\ n < 2 EXP k
            ==> bitsize (2 EXP k * m + n) = k + bitsize m) /\
   (!k m n. ~(m = 0) /\ n < 2 EXP k
            ==> bitsize (m * 2 EXP k + n) = k + bitsize m) /\
   (!k m n. ~(m = 0) /\ n < 2 EXP k
            ==> bitsize (n + 2 EXP k * m) = k + bitsize m) /\
   (!k m n. ~(m = 0) /\ n < 2 EXP k
            ==> bitsize (n + m * 2 EXP k) = k + bitsize m)`,
  MATCH_MP_TAC(TAUT `(p ==> q) /\ p ==> p /\ q`) THEN CONJ_TAC THENL
   [REWRITE_TAC[MULT_SYM; ADD_SYM; DISJ_SYM]; REPEAT STRIP_TAC] THEN
  REWRITE_TAC[GSYM LE_ANTISYM] THEN CONJ_TAC THENL
   [REWRITE_TAC[BITSIZE_LE] THEN TRANS_TAC LTE_TRANS `2 EXP k * (m + 1)` THEN
    REWRITE_TAC[EXP_ADD; LE_MULT_LCANCEL; EXP_EQ_0; ARITH_EQ] THEN
    REWRITE_TAC[ARITH_RULE `m + 1 <= r <=> m < r`; BITSIZE] THEN
    ASM_ARITH_TAC;
    TRANS_TAC LE_TRANS `bitsize(2 EXP k * m)` THEN CONJ_TAC THENL
     [ASM_REWRITE_TAC[BITSIZE_MULT; LE_REFL];
      MATCH_MP_TAC BITSIZE_MONO THEN ARITH_TAC]]);;

let BITSIZE_DIV = prove
 (`!n k. bitsize(n DIV 2 EXP k) = bitsize n - k`,
  REPEAT GEN_TAC THEN REWRITE_TAC[BITSIZE_UNIQUE] THEN
  SIMP_TAC[RDIV_LT_EQ; LE_RDIV_EQ;  EXP_EQ_0; ARITH_EQ] THEN
  ASM_CASES_TAC `bitsize n <= k` THENL
   [ASM_SIMP_TAC[ARITH_RULE `n <= k ==> n - k = 0`] THEN
    REWRITE_TAC[CONJUNCT1 LT; MULT_CLAUSES; EXP] THEN
    TRANS_TAC LTE_TRANS `2 EXP bitsize n` THEN
    ASM_REWRITE_TAC[BITSIZE; LE_EXP] THEN ASM_ARITH_TAC;
    ASM_SIMP_TAC[GSYM EXP_ADD; BITSIZE;
                 ARITH_RULE `~(n:num <= k) ==> k + n - k = n`] THEN
    ASM_SIMP_TAC[ARITH_RULE `~(n:num <= k) ==> (j < n - k <=> k + j < n)`] THEN
    REWRITE_TAC[ARITH_RULE `a < b <=> a + 1 <= b`; LE_BITSIZE] THEN
    REWRITE_TAC[ADD_SUB; ADD_EQ_0; ARITH_EQ]]);;

let BITSIZE_CONV =
  let rec bitfun k n =
    if n =/ num_0 then k
    else bitfun (k + 1) (quo_num n num_2) in
  fun tm ->
   (match tm with
      Comb(Const("bitsize",_),ntm) when is_numeral ntm ->
        let ktm = mk_small_numeral(bitfun 0 (dest_numeral ntm)) in
        let th = SPECL [ntm;ktm] BITSIZE_UNIQUE_EQ in
        EQT_ELIM(CONV_RULE (RAND_CONV NUM_REDUCE_CONV) th)
    | _ -> failwith "BITSIZE_CONV");;