> I tell new programmers, "ALWAYS use meaningful variable names and NEVER use 
> magic numbers".

That does help, but it is not the end. Some magic numbers are more clear 
when used magically than when #defined somewhere. This 2 should *not* be
#defined somewhere else:

n = n << 2; // multiply by 4 to get the word offset

In assembly, registers don't have meaningful names :( But this is a few 
parts of a graphics LCD driver:

    #define R_IOSET     R5
    #define R_IOCLR     R6
    #define R_SET_ALL   R7
    #define R_XCLR      R8
    #define R_MASK      R9
    #define R_TEMP      R10

    LDR R_IOCLR,   =MKT_IO0CLR
    LDR R_IOSET,   =MKT_IO0SET
    LDR R_SET_ALL, =SET_ALL
    LDR R_XCLR,    =SET_XSCL
    LDR R_MASK,    =SET_DATA

       // set XSCL and D0..D3
       STR R_SET_ALL, [ R_IOSET ]

       // shift 4 data bits to the correct position
       // and mask all other bits off
       AND R_TEMP, R_MASK, \REG, lsl #GLCD_D0

       // write D0..D3
       STR R_TEMP, [ R_IOCLR ]


-- 

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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