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## 3.2 Nomenclature and Types

In this manual, *integer* usually means a multiple precision integer, as
defined by the GMP library. The C data type for such integers is `mpz_t`

.
Here are some examples of how to declare such integers:

mpz_t sum; struct foo { mpz_t x, y; }; mpz_t vec[20];

*Rational number* means a multiple precision fraction. The C data type
for these fractions is `mpq_t`

. For example:

mpq_t quotient;

*Floating point number* or *Float* for short, is an arbitrary precision
mantissa with a limited precision exponent. The C data type for such objects
is `mpf_t`

. For example:

mpf_t fp;

The floating point functions accept and return exponents in the C type
`mp_exp_t`

. Currently this is usually a `long`

, but on some systems
it’s an `int`

for efficiency.

A *limb* means the part of a multi-precision number that fits in a single
machine word. (We chose this word because a limb of the human body is
analogous to a digit, only larger, and containing several digits.) Normally a
limb is 32 or 64 bits. The C data type for a limb is `mp_limb_t`

.

Counts of limbs of a multi-precision number represented in the C type
`mp_size_t`

. Currently this is normally a `long`

, but on some
systems it’s an `int`

for efficiency, and on some systems it will be
`long long`

in the future.

Counts of bits of a multi-precision number are represented in the C type
`mp_bitcnt_t`

. Currently this is always an `unsigned long`

, but on
some systems it will be an `unsigned long long`

in the future.

*Random state* means an algorithm selection and current state data. The C
data type for such objects is `gmp_randstate_t`

. For example:

gmp_randstate_t rstate;

Also, in general `mp_bitcnt_t`

is used for bit counts and ranges, and
`size_t`

is used for byte or character counts.

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