if.mac

; if.mac - if/else/endif conditional block macros

; 'if' takes one argument, a condition code.
; if the condition is true, the block is executed
; otherwise the else block is executed (if there is one)
;
; these macros are meant for short blocks only.
; they use short jump instructions, which have a range
; of +/- 127 bytes or about 50 instructions max.
;
; example:
;
;     cmp ax,0
;     if l
;         mov ax,0
;     endif
;
; translates to
;
;     cmp ax,0
;     jnl .label
;     mov ax,0
;   .label:

; adapted from https://www.nasm.us/doc/nasmdoc4.html#section-4.7.6

%macro if 1
    %push if
    j%-1 %$ifnot
%endmacro

%macro else 0
    %ifctx if
        %repl else
        jmp short %$ifend
        align 2
        %$ifnot:
    %else
        %error "expected 'if' before 'else'"
    %endif
%endmacro

%macro endif 0
    %ifctx else
        %$ifend:
        %pop else
    %else
        %$ifnot:
        %pop if
    %endif
%endmacro

; vim: syntax=nasm