From: NoEmail@nospicedham.trraxvfeqa.prg   
      
   On Tue, 24 Apr 2018 16:20:47 -0700   
   bilsch  wrote:   
      
   > On 04/24/2018 04:04 AM, Bartc wrote:   
   > > On 24/04/2018 10:48, bilsch wrote:   
      
   > >> The boot sector jumps to this code.   
   > >> It should print junk6789 but prints only j   
   > >> Why it not print junk6789 ?   TIA.   Bill S.     
   > >      
   > >>   
   > >> pbuf    times 80 db 0   
   > >> string    db 'junk'     
   > >      
   > >>            mov si,pbuf   
   > >>            mov di,string   
   > >> lup8:     mov al,[di]   
   > >>            mov byte[si],al   
   > >>            inc si   
   > >>            inc di   
   > >>            cmp di,4   
   > >>            jbe lup8     
   > >    
   > > di starts at label 'string'. Is that address 0? If not then   
   > > comparing it with 4 looks odd.   
   > >    
   > > If string has an address of at least 80 as seems likely, then this   
   > > will compare false and only one character is copied to the buffer.   
   > >      
   >    
   > Indeed.  Here's the fix to the code above.  It prints 'junk' but not    
   > 'junk6789'.  My real question is why doesn't it print the 6789 part?   
   >    
   > string    db 'junk',0   
   >    
   >            mov si,pbuf   
   >            mov di,string   
   > lup8:     mov al,[di]   
   >            cmp al,0   
   >            jz  ovr1   
   >            move byte[si],al   
   >            inc si   
   >            inc di   
   >            jmp lup8   
   > ovr1:   
   >    
      
   Your 'junk' loop at 'lup8' already increments 'si' _after_ storing al,   
   and then you increment 'si' again at 'xo5', but /prior/ to storing 'al'.   
   So, you've skipped copying a character into one location.  Since pbuf   
   buffer is zero'd initially, you've "inserted" a nul character between   
   'junk' and '6789', due to this skip or off-by-one error.  Your prstr   
   routine terminates at nul characters, which then skips everything after   
   'junk' since 'junk' is followed by a nul character.  I.e., the 'inc si'   
   at 'xo5' should be below the next instruction.   
      
      
   Rod Pemberton   
   --    
   I believe in the right to life.  That's why I oppose gun control.   
      
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