Routines 
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Used by the routine at compare.
The address of this routine is found in the table of addresses. It is called via the calculator literal +01 by the routines at BEEP, OPEN, FOR, NEXT_LOOP, CIRCLE, DRAW, CD_PRMS1, INT_TO_FP, PRINT_FP, series, n_mod_m, int, ln, get_argt, tan, atn and to_power.
This binary operation 'exchanges' the first number with the second number, i.e. the topmost two numbers on the calculator stack are exchanged.


exchange  343C  LD B,$05  There are five bytes involved.  
SWAP_BYTE  343E  LD A,(DE)  Each byte of the second number.  
343F  LD C,(HL)  Each byte of the first number.  
3440  EX DE,HL  Switch source and destination.  
3441  LD (DE),A  Now to the first number.  
3442  LD (HL),C  Now to the second number.  
3443  INC HL  Move to consider the next pair of bytes.  
3444  INC DE  
3445  DJNZ SWAP_BYTE  Exchange the five bytes.  
3447  EX DE,HL  Get the pointers correct as 5 is an odd number.  
3448  RET  Finished. 
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