Messages in this thread Patch in this message | | | From | Rusty Russell <> | Subject | [PATCH 4/6] typesafe: cast_if_type to allow macros functions which take more than one type. | Date | Sun, 20 Jan 2008 20:51:42 +1100 |
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To create functions which can take two types, but still warn on any other types, we need a way of casting one type and no others.
To make things more complex, it should correctly handle function args, NULL, and be usable in initializers.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff -r e6626cc7bdc2 include/linux/compiler-gcc.h --- a/include/linux/compiler-gcc.h Sun Jan 20 18:51:51 2008 +1100 +++ b/include/linux/compiler-gcc.h Sun Jan 20 18:57:14 2008 +1100 @@ -53,3 +53,20 @@ #define noinline __attribute__((noinline)) #define __attribute_const__ __attribute__((__const__)) #define __maybe_unused __attribute__((unused)) + +/** + * cast_if_type - allow an alternate type + * @expr: the expression to optionally cast + * @oktype: the type to allow. + * @desttype: the type to cast to. + * + * This is used to accept a particular alternate type for an expression: + * because any other types will not be cast, they will cause a warning as + * normal. + * + * Note that the unnecessary trinary forces functions to devolve into + * function pointers as users expect. */ +#define cast_if_type(expr, oktype, desttype) \ + __builtin_choose_expr(__builtin_types_compatible_p(typeof(1?(expr):NULL), \ + oktype), \ + (desttype)(expr), (expr)) diff -r e6626cc7bdc2 include/linux/compiler-intel.h --- a/include/linux/compiler-intel.h Sun Jan 20 18:51:51 2008 +1100 +++ b/include/linux/compiler-intel.h Sun Jan 20 18:57:14 2008 +1100 @@ -29,3 +29,5 @@ #endif #define uninitialized_var(x) x + +#define cast_if_type(expr, oktype, desttype) ((desttype)(expr))
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