From: Mateusz Viste <mate...@nospam.viste.fr> Hi Tom,
That's nice of you to provide the explanation. I didn't read it completely (too lazy), nor understand it fully (too stupid), but the other clueless guy might find it interesting that he was only half wrong. At the end of the day, I will keep using "JZ SHORT" anyway, 'cause that just works for me. cheers, Mateusz On Tue, 11 Apr 2017 12:33:17 +0200, Tom Ehlert wrote: >>>> Unless I'm mistaken, conditional jumps on 8086 don't go beyond -128 >>>> .. >>>> 127 (signed) byte range. Hence the billions of workarounds (TASM >>>> "jumps", MASM "option ljmp", etc). > right. > >>> I won't argue about what opcode is or is not available on 8086, since >>> I did not bother decoding their exact meaning. > > meaning 'I am a lazy, clueless guy, but write anyway ...' > >>> I do see however that (NASM at least) can assemble JZ and JZ SHORT in >>> two very different forms, JZ SHORT being significantly shorter. >>> >>> 5 00000000 B80100 mov ax, 1 6 00000003 48 dec >>> ax 7 00000004 746A jz short gameover >>> >>> 5 00000000 B80100 mov ax, 1 6 00000003 48 dec >>> ax 7 00000004 7503E9DD01 jz gameover >>> >>> Of course NASM always uses the short form whenever it's possible, but >>> when the jump is too far away it silently uses the longer form, hence >>> the need to always specify SHORT if one wants to be sure what's going >>> on. > >> AFAIK, > meaning 'I am completely clueless , but offer my unfounded opinion > anyway ...' > >> the longer one is 386+ only, hence not available with "cpu 8086". Thus, >> if it still quietly assembles, that is a bug (but I thought that was >> long-ago fixed/avoided). > > the longer one is 2 instructions instead, automatically generated by > NASM because the intended jump goes farther then 127 bte > > > c:\>debug -e 100 1430:0100 00.75 00.03 00.e9 00.dd 00.01 -u 100 > 1430:0100 7503 JNZ 0105 1430:0102 E9DD01 JMP > 02E2 > > > Tom ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user --- Internet Rex 2.29 * Origin: capcity2.synchro.net - 502/875-8938 (276:10/901) --- Synchronet 3.15a-Linux ListGate 1.3 * Capitol City Online - Frankfort, KY - telnet://capitolcityonline.net ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
