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Text Generation
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Text
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language-modeling
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English
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100K - 1M
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File size: 7,240 Bytes
4365a98 |
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(* ========================================================================= *)
(* 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");;
|