[Testing for zero]                                     [Assembler][/][8086]

If a routine gives back the result in a register and its value is 0 on
error and 1 on success, the ordinary

        or      ax,ax
        je      error

There are two things to note. First, use TEST instead of OR. This does not
write the result back to the register. There is however a better solution
that is smaller:

        dec     ax
        jne     error

For example, the XMS driver reports the errors this way. Is it fair that
testing a register=0 is longer than testing if it is 1 or -1?
                                                     Gem writer: Ervin Toth
                                                   last updated: 1998-03-16
