Fibonacci in ALGOL 60

Welcome to the Fibonacci in ALGOL 60 page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

begin
    procedure usage;
    begin
        outstring(1, "Usage: please input the count of fibonacci numbers to output\n");
        stop
    end usage;

    comment Input a digit character from stdin and return the following:
        - "0" to "9" maps to 0 to 9
        - "+" maps to 10
        - "-" maps to 11
        - whitespace maps to 12
        - null byte maps to -1
        - invalid bytes map to -2;
    integer procedure indigit;
    begin
        comment Mapping:
            - "0" to "9" maps to 1 to 10
            - "+" maps to 11
            - "-" maps to 12
            - "\t" maps to 13
            - "\r" maps to 14
            - "\n" maps to 15
            - " " maps to 16
            - null byte maps to 17
            - invalid byte maps 0;
        integer ch;
        inchar(0, "0123456789+-\t\r\n ", ch);
        if ch < 1 then ch := -2
        else if ch < 13 then ch := ch - 1
        else if ch < 17 then ch := 12
        else ch := -1;
        indigit := ch
    end indigit;

    comment Input an integer from stdin into 'result' and parse it.
        The last character is read into 'ch'.
        return true if integer is valid, false otherwise;
    boolean procedure inValidInteger(result, ch);
    integer result, ch;
    begin
        boolean valid;
        integer s;

        result := 0;
        valid := false;
        s := 1;

        comment Ignore whitespace;
    whiteloop:
        ch := indigit;
        if ch = 12 then goto whiteloop;

        comment Process signs: ignore "+" and invert sign if "-";
    signloop:
        if ch = 10 | ch = 11 then
        begin
            if ch = 11 then s := -s;
            ch := indigit;
            goto signloop
        end;

        comment Indicate valid if "0" to "9";
        if ch >= 0 & ch <= 9 then valid := true;

        comment Process digits: update value;
    valueloop:
        if ch >= 0 & ch <= 9 then
        begin
            comment Invalid if overflow or underflow;
            if (s > 0 & (maxint - ch) % 10 < result) |
                (s < 0 & (-1 - maxint + ch) % 10 > result) then valid := false;
            
            result := result * 10 + s * ch;
            ch := indigit;
            goto valueloop
        end;

        comment Ignore characters until end of argument. Indicate invalid
            if not whitespace;
    ignoreloop:
        if ch != -1 then
        begin
            if ch != 12 then valid := false;
            ch := indigit;
            goto ignoreloop
        end;

        inValidInteger := valid
    end inValidInteger;

    comment Output integer without space. This is needed since ALGOL60
        'outinteger' automatically adds a space after the integer.
        Source: 'outinteger' function source code in Appendix 2 of
        https://www.algol60.org/reports/algol60_mr.pdf;
    procedure outIntegerNoSpace(x);
    value x;
    integer x;
    begin
        procedure digits(x);
        value x;
        integer x;
        begin
            integer d;
            d := x % 10;
            x := x - 10 * d;
            if d != 0 then digits(d);
            outchar(1, "0123456789", iabs(x) + 1)
        end digits;
        if x < 0 then outstring(1, "-");
        digits(x)
    end outIntegerNoSpace;

    procedure fibonacci(n);
    value n;
    integer n;
    begin
        integer a, b, c, i;

        a := 0;
        b := 1;
        for i := 1 step 1 until n do
        begin
            c := a + b;
            a := b;
            b := c;
            outIntegerNoSpace(i);
            outstring(1, ": ");
            outIntegerNoSpace(a);
            outstring(1, "\n")
        end
    end fibonacci;

    integer argc, result, ch;

    comment Get number of parameters. Exit if too few;
    ininteger(0, argc);
    if argc < 1 then usage;

    comment Get integer value from 1st argument. Exit if invalid or
        negative;
    if !inValidInteger(result, ch) | result < 0 then usage;

    comment Output Fibonacci values;
    fibonacci(result)
end

Fibonacci in ALGOL 60 was written by:

• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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