-1

Hello everyone and thanks for trying to solve this exercise,I know that box al has the value ff, and in the box of bl has the value 03

but when iam doing the cmp al,bl: its not like (al-bl) and 255-3 its 252 Which means it's bigger so why when iam run this code on emu8086 It does not make a jump to L1 Instead he went into the order inc;

(i think its maybe something with the msb i dont know)

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Jester
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Hai Vaknin
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  • `JG` is signed arithmetic so your `255` is actually interpreted as `-1` which is not greater than `3`. If you want unsigned, use `JA`. – Jester Dec 01 '17 at 17:57
  • its because the most significant bit is 1? – Hai Vaknin Dec 01 '17 at 17:59
  • Bit, not byte. But yes. – Jester Dec 01 '17 at 18:02
  • If you had did some research you would have found the solution ***JG:*** http://www.electronics.dit.ie/staff/tscarff/8086_instruction_set/8086_instruction_set.html#JG ***JA*** http://www.electronics.dit.ie/staff/tscarff/8086_instruction_set/8086_instruction_set.html#JA – Ahtisham Dec 01 '17 at 19:57

1 Answers1

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The jg instruction indicates that the comparison is signed. This means that your 0xff will be interpreted as -1 as a one's complement value.

The ja instruction performs an unsigned comparison. You will find that this works as you expect.

David Hoelzer
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