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(************************************************************************)
(* v * The Coq Proof Assistant / The Coq Development Team *)
(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2011 *)
(* \VV/ **************************************************************)
(* // * This file is distributed under the terms of the *)
(* * GNU Lesser General Public License Version 2.1 *)
(************************************************************************)
(** [Big] : a wrapper around ocaml [Big_int] with nicer names,
and a few extraction-specific constructions *)
(** To be linked with [nums.(cma|cmxa)] *)
open Big_int
type big_int = Big_int.big_int
(** The type of big integers. *)
let zero = zero_big_int
(** The big integer [0]. *)
let one = unit_big_int
(** The big integer [1]. *)
let two = big_int_of_int 2
(** The big integer [2]. *)
(** {6 Arithmetic operations} *)
let opp = minus_big_int
(** Unary negation. *)
let abs = abs_big_int
(** Absolute value. *)
let add = add_big_int
(** Addition. *)
let succ = succ_big_int
(** Successor (add 1). *)
let add_int = add_int_big_int
(** Addition of a small integer to a big integer. *)
let sub = sub_big_int
(** Subtraction. *)
let pred = pred_big_int
(** Predecessor (subtract 1). *)
let mult = mult_big_int
(** Multiplication of two big integers. *)
let mult_int = mult_int_big_int
(** Multiplication of a big integer by a small integer *)
let square = square_big_int
(** Return the square of the given big integer *)
let sqrt = sqrt_big_int
(** [sqrt_big_int a] returns the integer square root of [a],
that is, the largest big integer [r] such that [r * r <= a].
Raise [Invalid_argument] if [a] is negative. *)
let quomod = quomod_big_int
(** Euclidean division of two big integers.
The first part of the result is the quotient,
the second part is the remainder.
Writing [(q,r) = quomod_big_int a b], we have
[a = q * b + r] and [0 <= r < |b|].
Raise [Division_by_zero] if the divisor is zero. *)
let div = div_big_int
(** Euclidean quotient of two big integers.
This is the first result [q] of [quomod_big_int] (see above). *)
let modulo = mod_big_int
(** Euclidean modulus of two big integers.
This is the second result [r] of [quomod_big_int] (see above). *)
let gcd = gcd_big_int
(** Greatest common divisor of two big integers. *)
let power = power_big_int_positive_big_int
(** Exponentiation functions. Return the big integer
representing the first argument [a] raised to the power [b]
(the second argument). Depending
on the function, [a] and [b] can be either small integers
or big integers. Raise [Invalid_argument] if [b] is negative. *)
(** {6 Comparisons and tests} *)
let sign = sign_big_int
(** Return [0] if the given big integer is zero,
[1] if it is positive, and [-1] if it is negative. *)
let compare = compare_big_int
(** [compare_big_int a b] returns [0] if [a] and [b] are equal,
[1] if [a] is greater than [b], and [-1] if [a] is smaller
than [b]. *)
let eq = eq_big_int
let le = le_big_int
let ge = ge_big_int
let lt = lt_big_int
let gt = gt_big_int
(** Usual boolean comparisons between two big integers. *)
let max = max_big_int
(** Return the greater of its two arguments. *)
let min = min_big_int
(** Return the smaller of its two arguments. *)
(** {6 Conversions to and from strings} *)
let to_string = string_of_big_int
(** Return the string representation of the given big integer,
in decimal (base 10). *)
let of_string = big_int_of_string
(** Convert a string to a big integer, in decimal.
The string consists of an optional [-] or [+] sign,
followed by one or several decimal digits. *)
(** {6 Conversions to and from other numerical types} *)
let of_int = big_int_of_int
(** Convert a small integer to a big integer. *)
let is_int = is_int_big_int
(** Test whether the given big integer is small enough to
be representable as a small integer (type [int])
without loss of precision. On a 32-bit platform,
[is_int_big_int a] returns [true] if and only if
[a] is between 2{^30} and 2{^30}-1. On a 64-bit platform,
[is_int_big_int a] returns [true] if and only if
[a] is between -2{^62} and 2{^62}-1. *)
let to_int = int_of_big_int
(** Convert a big integer to a small integer (type [int]).
Raises [Failure "int_of_big_int"] if the big integer
is not representable as a small integer. *)
(** Functions used by extraction *)
let double x = mult_int 2 x
let doubleplusone x = succ (double x)
let nat_case fO fS n = if sign n <= 0 then fO () else fS (pred n)
let positive_case f2p1 f2p f1 p =
if le p one then f1 () else
let (q,r) = quomod p two in if eq r zero then f2p q else f2p1 q
let n_case fO fp n = if sign n <= 0 then fO () else fp n
let z_case fO fp fn z =
let s = sign z in
if s = 0 then fO () else if s > 0 then fp z else fn (opp z)
let compare_case e l g x y =
let s = compare x y in if s = 0 then e else if s<0 then l else g
let nat_rec fO fS =
let rec loop acc n =
if sign n <= 0 then acc else loop (fS acc) (pred n)
in loop fO
let positive_rec f2p1 f2p f1 =
let rec loop n =
if le n one then f1
else
let (q,r) = quomod n two in
if eq r zero then f2p (loop q) else f2p1 (loop q)
in loop
let z_rec fO fp fn = z_case (fun _ -> fO) fp fn
|
