[thirdparty/gcc.git] / gcc / doc / gcc / extensions-to-the-c-language-family / double-word-integers.rst

..
  Copyright 1988-2022 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the copyright.rst file.

.. index:: long long data types, double-word arithmetic, multiprecision arithmetic, LL integer suffix, ULL integer suffix

.. _long-long:

Double-Word Integers
********************

ISO C99 and ISO C++11 support data types for integers that are at least
64 bits wide, and as an extension GCC supports them in C90 and C++98 modes.
Simply write ``long long int`` for a signed integer, or
``unsigned long long int`` for an unsigned integer.  To make an
integer constant of type ``long long int``, add the suffix :samp:`LL`
to the integer.  To make an integer constant of type ``unsigned long
long int``, add the suffix :samp:`ULL` to the integer.

You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports a fullword-to-doubleword widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC.

There may be pitfalls when you use ``long long`` types for function
arguments without function prototypes.  If a function
expects type ``int`` for its argument, and you pass a value of type
``long long int``, confusion results because the caller and the
subroutine disagree about the number of bytes for the argument.
Likewise, if the function expects ``long long int`` and you pass
``int``.  The best way to avoid such problems is to use prototypes.
Commit	Line	Data
c63539ff ML	1	..
	2	Copyright 1988-2022 Free Software Foundation, Inc.
	3	This is part of the GCC manual.
	4	For copying conditions, see the copyright.rst file.
	5
	6	.. index:: long long data types, double-word arithmetic, multiprecision arithmetic, LL integer suffix, ULL integer suffix
	7
	8	.. _long-long:
	9
	10	Double-Word Integers
	11	********************
	12
	13	ISO C99 and ISO C++11 support data types for integers that are at least
	14	64 bits wide, and as an extension GCC supports them in C90 and C++98 modes.
	15	Simply write ``long long int`` for a signed integer, or
	16	``unsigned long long int`` for an unsigned integer. To make an
	17	integer constant of type ``long long int``, add the suffix :samp:`LL`
	18	to the integer. To make an integer constant of type ``unsigned long
	19	long int``, add the suffix :samp:`ULL` to the integer.
	20
	21	You can use these types in arithmetic like any other integer types.
	22	Addition, subtraction, and bitwise boolean operations on these types
	23	are open-coded on all types of machines. Multiplication is open-coded
	24	if the machine supports a fullword-to-doubleword widening multiply
	25	instruction. Division and shifts are open-coded only on machines that
	26	provide special support. The operations that are not open-coded use
	27	special library routines that come with GCC.
	28
	29	There may be pitfalls when you use ``long long`` types for function
	30	arguments without function prototypes. If a function
	31	expects type ``int`` for its argument, and you pass a value of type
	32	``long long int``, confusion results because the caller and the
	33	subroutine disagree about the number of bytes for the argument.
	34	Likewise, if the function expects ``long long int`` and you pass
3ed1b4ce	35	``int``. The best way to avoid such problems is to use prototypes.