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Module Z

module Z: sig .. end
Integers.

This modules provides arbitrary-precision integers. Small integers internally use a regular OCaml int. When numbers grow too large, we switch transparently to GMP numbers (mpn numbers fully allocated on the OCaml heap).

This interface is rather similar to that of Int32 and Int64, with some additional functions provided natively by GMP (GCD, square root, pop-count, etc.).

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).


Toplevel



For an optimal experience with the ocaml interactive toplevel, the magic commands are: 

    #load "zarith.cma";;
    #install_printer Z.pp_print;;

Alternatively, using the new Zarith_top toplevel module, simply: 

    #require "zarith.top";;


Types


type t
Type of integers of arbitrary length.
exception Overflow
Raised by conversion functions when the value cannot be represented in the destination type.

Construction


val zero : t
The number 0.
val one : t
The number 1.
val minus_one : t
The number -1.
val of_int : int -> t
Converts from a base integer.
val of_int32 : int32 -> t
Converts from a 32-bit integer.
val of_int64 : int64 -> t
Converts from a 64-bit integer.
val of_nativeint : nativeint -> t
Converts from a native integer.
val of_float : float -> t
Converts from a floating-point value. The value is truncated (rounded towards zero). Raises Overflow on infinity and NaN arguments.
val of_string : string -> t
Converts a string to an integer. An optional - prefix indicates a negative number, while a + prefix is ignored. An optional prefix 0x, 0o, or 0b (following the optional - or + prefix) indicates that the number is, represented, in hexadecimal, octal, or binary, respectively. Otherwise, base 10 is assumed. (Unlike C, a lone 0 prefix does not denote octal.) Raises an Invalid_argument exception if the string is not a syntactically correct representation of an integer.
val of_substring : string -> pos:int -> len:int -> t
of_substring s ~pos ~len is the same as of_string (String.sub s pos len)
val of_string_base : int -> string -> t
Parses a number represented as a string in the specified base, with optional - or + prefix. The base must be between 2 and 16.
val of_substring_base : int -> string -> pos:int -> len:int -> t
of_substring_base base s ~pos ~len is the same as of_string_base base (String.sub s pos len)

Basic arithmetic operations


val succ : t -> t
Returns its argument plus one.
val pred : t -> t
Returns its argument minus one.
val abs : t -> t
Absolute value.
val neg : t -> t
Unary negation.
val add : t -> t -> t
Addition.
val sub : t -> t -> t
Subtraction.
val mul : t -> t -> t
Multiplication.
val div : t -> t -> t
Integer division. The result is truncated towards zero and obeys the rule of signs. Raises Division_by_zero if the divisor (second argument) is 0.
val rem : t -> t -> t
Integer remainder. Can raise a Division_by_zero. The result of rem a b has the sign of a, and its absolute value is strictly smaller than the absolute value of b. The result satisfies the equality a = b * div a b + rem a b.
val div_rem : t -> t -> t * t
Computes both the integer quotient and the remainder. div_rem a b is equal to (div a b, rem a b). Raises Division_by_zero if b = 0.
val cdiv : t -> t -> t
Integer division with rounding towards +oo (ceiling). Can raise a Division_by_zero.
val fdiv : t -> t -> t
Integer division with rounding towards -oo (floor). Can raise a Division_by_zero.
val ediv_rem : t -> t -> t * t
Euclidean division and remainder. ediv_rem a b returns a pair (q, r) such that a = b * q + r and 0 <= r < |b|. Raises Division_by_zero if b = 0.
val ediv : t -> t -> t
Euclidean division. ediv a b is equal to fst (ediv_rem a b). The result satisfies 0 <= a - b * ediv a b < |b|. Raises Division_by_zero if b = 0.
val erem : t -> t -> t
Euclidean remainder. erem a b is equal to snd (ediv_rem a b). The result satisfies 0 <= erem a b < |b| and a = b * ediv a b + erem a b. Raises Division_by_zero if b = 0.
val divexact : t -> t -> t
divexact a b divides a by b, only producing correct result when the division is exact, i.e., when b evenly divides a. It should be faster than general division. Can raise a Division_by_zero.

Bit-level operations



For all bit-level operations, negative numbers are considered in 2's complement representation, starting with a virtual infinite number of 1s.
val logand : t -> t -> t
Bitwise logical and.
val logor : t -> t -> t
Bitwise logical or.
val logxor : t -> t -> t
Bitwise logical exclusive or.
val lognot : t -> t
Bitwise logical negation. The identity lognot a=-a-1 always hold.
val shift_left : t -> int -> t
Shifts to the left. Equivalent to a multiplication by a power of 2. The second argument must be non-negative.
val shift_right : t -> int -> t
Shifts to the right. This is an arithmetic shift, equivalent to a division by a power of 2 with rounding towards -oo. The second argument must be non-negative.
val shift_right_trunc : t -> int -> t
Shifts to the right, rounding towards 0. This is equivalent to a division by a power of 2, with truncation. The second argument must be non-negative.
val numbits : t -> int
Returns the number of significant bits in the given number. If x is zero, numbits x returns 0. Otherwise, numbits x returns a positive integer n such that 2^{n-1} <= |x| < 2^n. Note that numbits is defined for negative arguments, and that numbits (-x) = numbits x.
val trailing_zeros : t -> int
Returns the number of trailing 0 bits in the given number. If x is zero, trailing_zeros x returns max_int. Otherwise, trailing_zeros x returns a nonnegative integer n which is the largest n such that 2^n divides x evenly. Note that trailing_zeros is defined for negative arguments, and that trailing_zeros (-x) = trailing_zeros x.
val testbit : t -> int -> bool
testbit x n return the value of bit number n in x: true if the bit is 1, false if the bit is 0. Bits are numbered from 0. Raise Invalid_argument if n is negative.
val popcount : t -> int
Counts the number of bits set. Raises Overflow for negative arguments, as those have an infinite number of bits set.
val hamdist : t -> t -> int
Counts the number of different bits. Raises Overflow if the arguments have different signs (in which case the distance is infinite).

Conversions



Note that, when converting to an integer type that cannot represent the converted value, an Overflow exception is raised.
val to_int : t -> int
Converts to a base integer. May raise Overflow.
val to_int32 : t -> int32
Converts to a 32-bit integer. May raise Overflow.
val to_int64 : t -> int64
Converts to a 64-bit integer. May raise Overflow.
val to_nativeint : t -> nativeint
Converts to a native integer. May raise Overflow.
val to_float : t -> float
Converts to a floating-point value. This function rounds the given integer according to the current rounding mode of the processor. In default mode, it returns the floating-point number nearest to the given integer, breaking ties by rounding to even.
val to_string : t -> string
Gives a human-readable, decimal string representation of the argument.
val format : string -> t -> string
Gives a string representation of the argument in the specified printf-like format. The general specification has the following form:

% [flags] [width] type

Where the type actually indicates the base:

Supported flags are:

Unlike the classic printf, all numbers are signed (even hexadecimal ones), there is no precision field, and characters that are not part of the format are simply ignored (and not copied in the output).
val fits_int : t -> bool
Whether the argument fits in a regular int.
val fits_int32 : t -> bool
Whether the argument fits in an int32.
val fits_int64 : t -> bool
Whether the argument fits in an int64.
val fits_nativeint : t -> bool
Whether the argument fits in a nativeint.

Printing


val print : t -> unit
Prints the argument on the standard output.
val output : Pervasives.out_channel -> t -> unit
Prints the argument on the specified channel. Also intended to be used as %a format printer in Printf.printf.
val sprint : unit -> t -> string
To be used as %a format printer in Printf.sprintf.
val bprint : Buffer.t -> t -> unit
To be used as %a format printer in Printf.bprintf.
val pp_print : Format.formatter -> t -> unit
Prints the argument on the specified formatter. Can be used as %a format printer in Format.printf and as argument to #install_printer in the top-level.

Ordering


val compare : t -> t -> int
Comparison. compare x y returns 0 if x equals y, -1 if x is smaller than y, and 1 if x is greater than y.

Note that Pervasive.compare can be used to compare reliably two integers only on OCaml 3.12.1 and later versions.

val equal : t -> t -> bool
Equality test.
val leq : t -> t -> bool
Less than or equal.
val geq : t -> t -> bool
Greater than or equal.
val lt : t -> t -> bool
Less than (and not equal).
val gt : t -> t -> bool
Greater than (and not equal).
val sign : t -> int
Returns -1, 0, or 1 when the argument is respectively negative, null, or positive.
val min : t -> t -> t
Returns the minimum of its arguments.
val max : t -> t -> t
Returns the maximum of its arguments.
val is_even : t -> bool
Returns true if the argument is even (divisible by 2), false if odd.
val is_odd : t -> bool
Returns true if the argument is odd, false if even.
val hash : t -> int
Hashes a number. This functions gives the same result as OCaml's polymorphic hashing function. The result is consistent with equality: if a = b, then hash a = hash b.

Elementary number theory


val gcd : t -> t -> t
Greatest common divisor. The result is always positive. Raises a Division_by_zero is either argument is null.
val gcdext : t -> t -> t * t * t
gcdext u v returns (g,s,t) where g is the greatest common divisor and g=us+vt. g is always positive. Raises a Division_by_zero is either argument is null.

Note: the function is based on the GMP mpn_gcdext function. The exact choice of s and t such that g=us+vt is not specified, as it may vary from a version of GMP to another (it has changed notably in GMP 4.3.0 and 4.3.1).

val lcm : t -> t -> t
Least common multiple. The result is always positive. Raises a Division_by_zero is either argument is null.
val powm : t -> t -> t -> t
powm base exp mod computes base^exp modulo mod. Negative exp are supported, in which case (base^-1)^(-exp) modulo mod is computed. However, if exp is negative but base has no inverse modulo mod, then a Division_by_zero is raised.
val powm_sec : t -> t -> t -> t
powm_sec base exp mod computes base^exp modulo mod. Unlike Z.powm, this function is designed to take the same time and have the same cache access patterns for any two same-size arguments. Used in cryptographic applications, it provides better resistance to side-channel attacks than Z.powm. The exponent exp must be positive, and the modulus mod must be odd. Otherwise, Invalid_arg is raised.
val invert : t -> t -> t
invert base mod returns the inverse of base modulo mod. Raises a Division_by_zero if base is not invertible modulo mod.
val probab_prime : t -> int -> int
probab_prime x r returns 0 if x is definitely composite, 1 if x is probably prime, and 2 if x is definitely prime. The r argument controls how many Miller-Rabin probabilistic primality tests are performed (5 to 10 is a reasonable value).
val nextprime : t -> t
Returns the next prime greater than the argument. The result is only prime with very high probability.

Powers


val pow : t -> int -> t
pow base exp raises base to the exp power. exp must be non-negative. Note that only exponents fitting in a machine integer are supported, as larger exponents would surely make the result's size overflow the address space.
val sqrt : t -> t
Returns the square root. The result is truncated (rounded down to an integer). Raises an Invalid_argument on negative arguments.
val sqrt_rem : t -> t * t
Returns the square root truncated, and the remainder. Raises an Invalid_argument on negative arguments.
val root : t -> int -> t
root base n computes the n-th root of exp. n must be non-negative.
val perfect_power : t -> bool
True if the argument has the form a^b, with b>1
val perfect_square : t -> bool
True if the argument has the form a^2.
val log2 : t -> int
Returns the base-2 logarithm of its argument, rounded down to an integer. If x is positive, log2 x returns the largest n such that 2^n <= x. If x is negative or zero, log2 x raise the Invalid_argument exception.
val log2up : t -> int
Returns the base-2 logarithm of its argument, rounded up to an integer. If x is positive, log2up x returns the smallest n such that x <= 2^n. If x is negative or zero, log2up x raise the Invalid_argument exception.

Representation


val size : t -> int
Returns the number of machine words used to represent the number.
val extract : t -> int -> int -> t
extract a off len returns a non-negative number corresponding to bits off to off+len-1 of b. Negative a are considered in infinite-length 2's complement representation.
val signed_extract : t -> int -> int -> t
signed_extract a off len extracts bits off to off+len-1 of b, as extract does, then sign-extends bit len-1 of the result (that is, bit off + len - 1 of a). The result is between - 2{^[len]-1} (included) and 2{^[len]-1} (excluded), and equal to extract a off len modulo 2{^len}.
val to_bits : t -> string
Returns a binary representation of the argument. The string result should be interpreted as a sequence of bytes, corresponding to the binary representation of the absolute value of the argument in little endian ordering. The sign is not stored in the string.
val of_bits : string -> t
Constructs a number from a binary string representation. The string is interpreted as a sequence of bytes in little endian order, and the result is always positive. We have the identity: of_bits (to_bits x) = abs x. However, we can have to_bits (of_bits s) <> s due to the presence of trailing zeros in s.

Prefix and infix operators



Classic (and less classic) prefix and infix int operators are redefined on t.

This makes it easy to typeset expressions. Using OCaml 3.12's local open, you can simply write Z.(~$2 + ~$5 * ~$10).

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
Truncated division div.
val (/>) : t -> t -> t
Ceiling division cdiv.
val (/<) : t -> t -> t
Flooring division fdiv.
val (/|) : t -> t -> t
Exact division div_exact.
val (mod) : t -> t -> t
Remainder rem.
val (land) : t -> t -> t
Bit-wise logical and logand.
val (lor) : t -> t -> t
Bit-wise logical inclusive or logor.
val (lxor) : t -> t -> t
Bit-wise logical exclusive or logxor.
val (~!) : t -> t
Bit-wise logical negation lognot.
val (lsl) : t -> int -> t
Bit-wise shift to the left shift_left.
val (asr) : t -> int -> t
Bit-wise shift to the right shift_right.
val (~$) : int -> t
Conversion from int of_int.
val ( ** ) : t -> int -> t
Power pow.
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).

Miscellaneous


val version : string
Library version (this file refers to version "1.5").