Implementing Alternation

There is no explicit support for alternation in assembly language. You must do it in pieces, as in the following. Say that registers $8 and $9 hold the values a and b.

        ...                #   
if:     beq  $8,$9,yes     # is a==b ?
        nop                #    no
        ...                #    false block
        ...                #    
        ...                #  
        j    endif
        nop
yes:    ...                #   yes
        ...                #   true block
        ...                #
endif:  nop                # always executed

Notice that the order of the true block and the false block is the opposite of what is usual in high level languages.

This is not the only way alternation can be implemented. You can put the true block first if you want (but then the branch statment must be changed). Also, testing the condition might be complicated and might involve several branches and other instructions that the flowchart does not show.