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## 5.1 Initialization Functions

The functions for integer arithmetic assume that all integer objects are
initialized. You do that by calling the function `mpz_init`

. For
example,

{ mpz_t integ; mpz_init (integ); … mpz_add (integ, …); … mpz_sub (integ, …); /* Unless the program is about to exit, do ... */ mpz_clear (integ); }

As you can see, you can store new values any number of times, once an object is initialized.

- Function:
*void***mpz_inits***(mpz_t*`x`, ...) Initialize a NULL-terminated list of

`mpz_t`

variables, and set their values to 0.

- Function:
*void***mpz_init2***(mpz_t*`x`, mp_bitcnt_t`n`) Initialize

`x`, with space for`n`-bit numbers, and set its value to 0. Calling this function instead of`mpz_init`

or`mpz_inits`

is never necessary; reallocation is handled automatically by GMP when needed.While

`n`defines the initial space,`x`will grow automatically in the normal way, if necessary, for subsequent values stored.`mpz_init2`

makes it possible to avoid such reallocations if a maximum size is known in advance.In preparation for an operation, GMP often allocates one limb more than ultimately needed. To make sure GMP will not perform reallocation for

`x`, you need to add the number of bits in`mp_limb_t`

to`n`.

- Function:
*void***mpz_clear***(mpz_t*`x`) Free the space occupied by

`x`. Call this function for all`mpz_t`

variables when you are done with them.

- Function:
*void***mpz_clears***(mpz_t*`x`, ...) Free the space occupied by a NULL-terminated list of

`mpz_t`

variables.

- Function:
*void***mpz_realloc2***(mpz_t*`x`, mp_bitcnt_t`n`) Change the space allocated for

`x`to`n`bits. The value in`x`is preserved if it fits, or is set to 0 if not.Calling this function is never necessary; reallocation is handled automatically by GMP when needed. But this function can be used to increase the space for a variable in order to avoid repeated automatic reallocations, or to decrease it to give memory back to the heap.

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