Hi!
 6-Feb-98 17:21 John Payson wrote about "Re: Accessing text strings.":

 >> > Yes, strings are a pain on the PIC.
    :(


 >> BTW, another useful trick when writing code that should be equivalent to
 >>   printf("Answer=%3d Result=%05D", answer, result);
 >> is to code it like this [more or less]; note that if there weren't very
 >> many printfs, it might be better to put more of the work in the "format"
 >> section and less in the library section.  Note that "Format" is designed
 >> to be used as a string in a string-print procedure.
 >>
 >> Format:
 >>         db      "Answer="
 >>         movlw   answer
 >>         call    IntPConvert
 >>         goto    BGetHund
 >>         goto    BGetTens
 >>         goto    GetOnes
 >>         db      " Result="
        .....
 >> IntPConvert:
 >>         bsf     blankflag
 >>         movwf   FSR
 >>         movf    IND,w
 >>         movwf   TempL
 >>         incf    IND
 >>         movf    IND,w
 >>         movwf   TempH
 >>         goto    Convert ; My wonderful bin->dec convert routine
        .....


    Unfortunatly, one should note that this code can't be used
exactly as a string. The string planned to be read is:
     0123456789     (index in "CALL ReadFormat")
    "Answer=ddd"..  (string to be read; ddd is the decimal value
                    of the two bytes pointed by answer)

Actually, we shell read "Answer=", but then some strange effects
will be produced. (I suppouse that "Convert" makes convertion only).

    If index==7 then instructions "movlw answer" and
"call IntPConvert" will be done. So, the value returned by
conversion rotine "Convert" will be obtained by caller instead
of the first digit of ansver (hundreds).

    If index==8 then only "call IntPConvert" will be done, and W
will cotain value of 8 (if "addwf PCL,f" is used). So, TempL and
TempH will be replaced with the values of SFR's 0x08 and 0x09
"Convert" routine will be called again. The value returned by
"Convert" will be included into the string too.

    The string will be like this:
     0123456789012      (index in CALL ReadFormat)
    "Answer=??ddd"..    (string; '?' is unpredictable chars
                        returned by "Convert")

    To avoid this one should perform additional increment by 2
the value of "index" in routine "Convert" or in code labeled
with "IntPConvert" (it is better, because routine "Convert"
remain unchanged and can be called with no connection with any
strings). But generally, nobody can know what variable was used
as index in "CALL ReadFormat". Thus we have to use the same
variable ("format_index") for every format string.

    Another method is to make some improvements. Every char of
the desired string should be represented by the only command. It
may be something like this:

Format:
        db      "Answer="

;        movlw   answer
;        call    IntPConvert
;        goto    BGetHund
        goto    GetAnswer_And_Hund  ;;  !!!

        goto    BGetTens
        goto    GetOnes
        db      " Result="
    .....

GetAnswer_And_Hund:
        movlw   answer
        call    IntPConvert
        goto    BGetHund

IntPConvert:
        bsf     blankflag
        movwf   FSR
        movf    IND,w
        movwf   TempL
        incf    IND
        movf    IND,w
        movwf   TempH
        goto    Convert ; My wonderful bin->dec convert routine
    .....

    Now if index==7 then "goto GetAnswer_And_Hund" will be
executed. The desired value vill be transfered into TempL,TempH;
"Convert" will be called and executed but returned value
ignored; then "goto BGetHund" will be executed and the digit of
hundreds of the desired number will be returned as a next char
of the string. The next call (index==8) will cause the
"goto BGetTens" executed and so on.


    I use method like described above for an interfacing to
formatted output library. But I don't build a "string-like" code.
Instead of this I build an "output list". Here is a siplified
example (FMT... are entry points of library routines; index of
current processing element is mantained in the library):

Example:
    goto    FMT_BLANK
    goto    proc_answer_string
    goto    proc_asnwer_value
    goto    FMT_BLANK   ; there are special entries for often used chars
    goto    FMT_COMMA   ;   like " .,;:+-*"
    goto    FMT_ENDLIST ; No comments :)

proc_answer_value:
    movlw   answer
    goto    FMT_03D_I   ; Use "%03d" coversion, "FMT..._I" means
                        ;   indirect addressing
proc_answer_string:
    movlw   high(answer_string)
    movwf   hi_addr
    movlw   low(answer_string)
    goto    FMT_S_ROM

answer_string:  db  "Answer=",0


    This example was mentioned as simplified because this
library has many other entry points. For example it is not
efficient to use FMT_03D_I in this case. There is another entry
(let us refer it as FMT_03D_I_ALT). It produce the same effect
as FMT_03D_I but index of current processing element will be
incremented by 2. So, we can eliminate one GoTo command and one
label. (It's not joke, total number of labels will be too high
and the risk of undetected mistypes will be very high too.) The
example became as follows:

    printf(" Answer=%03d, ", *answer);

Example:
    goto    FMT_BLANK
    goto    proc_answer_string
    movlw   answer
    goto    FMT_03D_I_ALT
    goto    proc_asnwer_value
    goto    FMT_COMMA   ; there are special entries for often used chars
    goto    FMT_BLANK   ;   like " .,;:+-*". It was not necessary to use
                        ;   this possibility here. It's illustration only
    goto    FMT_ENDLIST         ; No comments :)

proc_answer_string:
    movlw   high(answer_string)
    movwf   hi_addr
    movlw   low(answer_string)
    goto    FMT_S_ROM

answer_string:  db  "Answer=",0

    Entry point FMT_S_ROM (and other string rotines) maintain
its own internal index (rather than index of the list elements)
for access to procesing string.



    This library can be used to implement more complicated
printfs. For example:

    printf("Status is \'%s\'", ok==0?"Failed":"OK!");
Actually will be implemented some other printf:
    printf("%s%s%c", "Status is \'", ok==0?"Failed":"OK!",'\'');

Example2:
    goto    proc_status_string
    goto    proc_status_report
    movlw   "'"
    goto    FMT_C_ALT