USR function (*solved*)

[britlion]

Testing the results of the USR function seems to come up with the right answers, but my "invert a graphic" sub seems to be breaking in strange ways.

Can't quite follow why:

Is it me doing something silly, or the compiler? It seems to miss a line off the top, and then write gibberish into the next one, before carrying on normally with the last six lines. Is it my emulator (spin)? or my program?

I just checked: Does the same thing in Spectaculator.
And "Print \b" seems to print a B missing the top before my sub even runs...

Code:

SUB fastcall hMirror (udg as uInteger)
ASM    
    
    ld b,8  
    hMirrorRotate:
      LD C,(HL)
      
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
      RR C
      RLA
    
      LD (HL),A
      
      INC HL
    DJNZ hMirrorRotate
      
END ASM
END SUB

CLS

PRINT "Address: ";USR "B"

PRINT "\b"
hMirror (USR"B")
PRINT "\b"