Re: Assembly macro with parameters

[David Daney <ddaney@avtrex.com>]

Fabrizio Fazzino wrote:
> After three months I still have the same problem...
> 
> Suppose I want to generate my own opcode, let's say 0xC4000000,
> inside a C program. Suppose this value is NOT a constant in
> the macro I want to write since it will contain three
> variable fields for the rd,rs,rt registers, so I need to calculate
> the opcode at least at compilation time (at runtime is NOT
> required).
> 
> Daniel suggested using .word and writing the function by hand,
> but which is the syntax I have to use?
> 
> #define myopcode(rs,rt,rd) { \
>   int opcode_number = 0xC4000000 | (rs<<21) | (rt<<16) | (rd<<11); \
>   char opcode_string[20]; \
>   sprintf(opcode_string, ".word 0x%X", opcode_number); \
>   asm(opcode_string); \
> }
> 

The arguments to the asm() statement are strings not char*.  They are 
evaluated at compile time not run time.

You will probably have to use the C preprocessor stringification and 
concatination operators ('#' and '##').

David Daney