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| -rw-r--r-- | docs/LanguageExtensions.rst | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst index 4d616f8097..f8dbb68519 100644 --- a/docs/LanguageExtensions.rst +++ b/docs/LanguageExtensions.rst @@ -1395,6 +1395,43 @@ correct code by avoiding expensive loops around implementation details of ``__sync_lock_test_and_set()``. The ``__sync_swap()`` builtin is a full barrier. +Multiprecision Arithmetic Builtins +---------------------------------- + +Clang provides a set of builtins which expose multiprecision arithmetic in a +manner amenable to C. They all have the following form: + +.. code-block:: c + + unsigned x = ..., y = ..., carryin = ..., carryout; + unsigned sum = __builtin_addc(x, y, carryin, &carryout); + +Thus one can form a multiprecision addition chain in the following manner: + +.. code-block:: c + + unsigned *x, *y, *z, carryin=0, carryout; + z[0] = __builtin_addc(x[0], y[0], carryin, &carryout); + carryin = carryout; + z[1] = __builtin_addc(x[1], y[1], carryin, &carryout); + carryin = carryout; + z[2] = __builtin_addc(x[2], y[2], carryin, &carryout); + carryin = carryout; + z[3] = __builtin_addc(x[3], y[3], carryin, &carryout); + +The complete list of builtins are: + +.. code-block:: c + + unsigned short __builtin_addcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout); + unsigned __builtin_addc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout); + unsigned long __builtin_addcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout); + unsigned long long __builtin_addcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout); + unsigned short __builtin_subcs (unsigned short x, unsigned short y, unsigned short carryin, unsigned short *carryout); + unsigned __builtin_subc (unsigned x, unsigned y, unsigned carryin, unsigned *carryout); + unsigned long __builtin_subcl (unsigned long x, unsigned long y, unsigned long carryin, unsigned long *carryout); + unsigned long long __builtin_subcll(unsigned long long x, unsigned long long y, unsigned long long carryin, unsigned long long *carryout); + .. _langext-__c11_atomic: __c11_atomic builtins |