Re: [Qemu-ppc] [Qemu-devel] [PATCH 02/31] dt: add helpers for 2, 3 and 4 cell adds

[Alexander Graf]

On 07.06.2012, at 01:45, David Gibson wrote:

> [snip]
>>> You mean internally? Yeah, probably. Externally? The point of these
>>> helpers is to make the code look less cluttered. We can already pass in
>>> an array just fine, but C is quite annoying about generating those on
>>> the fly, while it's easy to pass in ints as parameters :)
>> 
>> Varargs?
> 
> Ugly and risky with standard C varargs (because an explicit length
> would be needed).  Could be done neatly with gcc macro varargs.

Could a combination of both like this work?

#include <stdio.h>
#include <stdarg.h>

#define __VA_NARG__(...) \
        (__VA_NARG_(_0, ## __VA_ARGS__, __RSEQ_N()) - 1)
#define __VA_NARG_(...) \
        __VA_ARG_N(__VA_ARGS__)
#define __VA_ARG_N( \
         _1, _2, _3, _4, _5, _6, _7, _8, _9,_10, \
        _11,_12,_13,_14,_15,_16,_17,_18,_19,_20, \
        _21,_22,_23,_24,_25,_26,_27,_28,_29,_30, \
        _31,_32,_33,_34,_35,_36,_37,_38,_39,_40, \
        _41,_42,_43,_44,_45,_46,_47,_48,_49,_50, \
        _51,_52,_53,_54,_55,_56,_57,_58,_59,_60, \
        _61,_62,_63,N,...) N
#define __RSEQ_N() \
        63, 62, 61, 60,                         \
        59, 58, 57, 56, 55, 54, 53, 52, 51, 50, \
        49, 48, 47, 46, 45, 44, 43, 42, 41, 40, \
        39, 38, 37, 36, 35, 34, 33, 32, 31, 30, \
        29, 28, 27, 26, 25, 24, 23, 22, 21, 20, \
        19, 18, 17, 16, 15, 14, 13, 12, 11, 10, \
         9,  8,  7,  6,  5,  4,  3,  2,  1,  0

#define PRINT_ELEMS(fdt, ...) print_elems(fdt, __VA_NARG__(__VA_ARGS__), 
__VA_ARGS__)

int print_elems(void *fdt, unsigned int count, ...)
{
    int i;
    va_list argp;

    va_start(argp, count);

    for (i = 0; i < count; i++)
        printf("%d -> %#x\n", i, va_arg(argp, int));

    va_end(argp);

    return 0;
}

int main(int argc, char **argv)
{
    PRINT_ELEMS(NULL, 1, 2, 3, 4);
    return 0;
}