package tezos-protocol-environment

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package tezos-protocol-environment
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Rationals.

This modules builds arbitrary precision rationals on top of arbitrary integers from module Z.

This file is part of the Zarith library http://forge.ocamlcore.org/projects/zarith . It is distributed under LGPL 2 licensing, with static linking exception. See the LICENSE file included in the distribution.

Copyright (c) 2010-2011 Antoine Miné, Abstraction project. Abstraction is part of the LIENS (Laboratoire d'Informatique de l'ENS), a joint laboratory by: CNRS (Centre national de la recherche scientifique, France), ENS (École normale supérieure, Paris, France), INRIA Rocquencourt (Institut national de recherche en informatique, France).

Types

type t = Q.t = {
  1. num : Z.t;
    (*

    Numerator.

    *)
  2. den : Z.t;
    (*

    Denominator, >= 0

    *)
}

A rational is represented as a pair numerator/denominator, reduced to have a non-negative denominator and no common factor. This form is canonical (enabling polymorphic equality and hashing). The representation allows three special numbers: inf (1/0), -inf (-1/0) and undef (0/0).

Construction

val make : Z.t -> Z.t -> t

make num den constructs a new rational equal to num/den. It takes care of putting the rational in canonical form.

val zero : t
val one : t
val minus_one : t

0, 1, -1.

val inf : t

1/0.

val minus_inf : t

-1/0.

val undef : t

0/0.

val of_bigint : Z.t -> t
val of_int : int -> t
val of_int32 : int32 -> t
val of_int64 : int64 -> t

Conversions from various integer types.

val of_ints : int -> int -> t

Conversion from an int numerator and an int denominator.

val of_string : string -> t

Converts a string to a rational. Plain integers, / separated integer ratios (with optional sign), decimal point and scientific notations are understood. Additionally, the special inf, -inf, and undef are recognized (they can also be typeset respectively as 1/0, -1/0, 0/0).

Inspection

val num : t -> Z.t

Get the numerator.

val den : t -> Z.t

Get the denominator.

Testing

type kind =
  1. | ZERO
    (*

    0

    *)
  2. | INF
    (*

    infinity, i.e. 1/0

    *)
  3. | MINF
    (*

    minus infinity, i.e. -1/0

    *)
  4. | UNDEF
    (*

    undefined, i.e., 0/0

    *)
  5. | NZERO
    (*

    well-defined, non-infinity, non-zero number

    *)

Rationals can be categorized into different kinds, depending mainly on whether the numerator and/or denominator is null.

val classify : t -> kind

Determines the kind of a rational.

val is_real : t -> bool

Whether the argument is non-infinity and non-undefined.

val sign : t -> int

Returns 1 if the argument is positive (including inf), -1 if it is negative (including -inf), and 0 if it is null or undefined.

val compare : t -> t -> int

compare x y compares x to y and returns 1 if x is strictly greater that y, -1 if it is strictly smaller, and 0 if they are equal. This is a total ordering. Infinities are ordered in the natural way, while undefined is considered the smallest of all: undef = undef < -inf <= -inf < x < inf <= inf. This is consistent with OCaml's handling of floating-point infinities and NaN.

OCaml's polymorphic comparison will NOT return a result consistent with the ordering of rationals.

val equal : t -> t -> bool

Equality testing. Unlike compare, this follows IEEE semantics: undef <> undef.

val min : t -> t -> t

Returns the smallest of its arguments.

val max : t -> t -> t

Returns the largest of its arguments.

val leq : t -> t -> bool

Less than or equal. leq undef undef resturns false.

val geq : t -> t -> bool

Greater than or equal. leq undef undef resturns false.

val lt : t -> t -> bool

Less than (not equal).

val gt : t -> t -> bool

Greater than (not equal).

Conversions

val to_bigint : t -> Z.t
val to_int : t -> int
val to_int32 : t -> int32
val to_int64 : t -> int64

Convert to integer by truncation. Raises a Divide_by_zero if the argument is an infinity or undefined. Raises a Z.Overflow if the result does not fit in the destination type.

val to_string : t -> string

Converts to human-readable, base-10, /-separated rational.

Arithmetic operations

In all operations, the result is undef if one argument is undef. Other operations can return undef: such as inf-inf, inf*0, 0/0.

val neg : t -> t

Negation.

val abs : t -> t

Absolute value.

val add : t -> t -> t

Addition.

val sub : t -> t -> t

Subtraction. We have sub x y = add x (neg y).

val mul : t -> t -> t

Multiplication.

val inv : t -> t

Inverse. Note that inv 0 is defined, and equals inf.

val div : t -> t -> t

Division. We have div x y = mul x (inv y), and inv x = div one x.

val mul_2exp : t -> int -> t

mul_2exp x n multiplies x by 2 to the power of n.

val div_2exp : t -> int -> t

div_2exp x n divides x by 2 to the power of n.

Printing

val pp_print : Format.formatter -> t -> unit

Prints the argument on the specified formatter. Also intended to be used as %a format printer in Format.printf.

Prefix and infix operators

Classic prefix and infix int operators are redefined on t.

val (~-) : t -> t

Negation neg.

val (~+) : t -> t

Identity.

val (+) : t -> t -> t

Addition add.

val (-) : t -> t -> t

Subtraction sub.

val (*) : t -> t -> t

Multiplication mul.

val (/) : t -> t -> t

Division div.

val (lsl) : t -> int -> t

Multiplication by a power of two mul_2exp.

val (asr) : t -> int -> t

Division by a power of two shift_right.

val (~$) : int -> t

Conversion from int.

val (//) : int -> int -> t

Creates a rational from two ints.

val (~$$) : Z.t -> t

Conversion from Z.t.

val (///) : Z.t -> Z.t -> t

Creates a rational from two Z.t.

val (=) : t -> t -> bool

Same as equal.

val (<) : t -> t -> bool

Same as lt.

val (>) : t -> t -> bool

Same as gt.

val (<=) : t -> t -> bool

Same as leq.

val (>=) : t -> t -> bool

Same as geq.

val (<>) : t -> t -> bool

a <> b is equivalent to not (equal a b).

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