Add Prime Number in ALGOL 60 (#5365)

Author: rzuckerm

archive/a/algol60/prime-number.alg

@@ -0,0 +1,127 @@
+begin
+    procedure usage;
+    begin
+        outstring(1, "Usage: please input a non-negative integer\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
+        - comma maps to 13
+        - 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
+            - "," mapps to 13
+            - "\t" maps to 14
+            - "\r" maps to 15
+            - "\n" maps to 16
+            - " " maps to 17
+            - null byte maps to 18
+            - invalid byte maps 0;
+        integer ch;
+        inchar(0, "0123456789+-,\t\r\n ", ch);
+        if ch < 1 then ch := -2
+        else if ch < 14 then ch := ch - 1
+        else if ch < 18 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;
+        for ch := indigit while ch = 12 do indigit;
+
+        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 Process digits: update value;
+    valueloop:
+        if ch >= 0 & ch <= 9 then
+        begin
+            comment Invalid if overflow or underflow;
+            valid := false;
+            if (s > 0 & (maxint - ch) % 10 < result) |
+                (s < 0 & (-1 - maxint + ch) % 10 > result) then goto done;
+
+            result := result * 10 + s * ch;
+            ch := indigit;
+            valid := true;
+            goto valueloop
+        end;
+
+        comment Ignore whitespace;
+        for ch := ch while ch = 12 do ch := indigit;
+
+    done:
+        inValidInteger := valid
+    end inValidInteger;
+
+    integer procedure mod(x, n);
+    value x, n;
+    integer x, n;
+    begin
+        mod := x - n * (x % n)
+    end mod;
+
+    boolean procedure isprime(x);
+    value x;
+    integer x;
+    begin
+        boolean result;
+        integer i, q;
+
+        result := x = 2 | (x > 2 & mod(x, 2) != 0);
+        if result then
+        begin
+            q := entier(sqrt(x));
+            for i := 3 step 2 until q do
+            begin
+                result := mod(x, i) != 0;
+                if !result then goto done
+            end
+        end;
+
+    done:
+        isprime := result
+    end isprime;
+
+    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, not
+        end of argument, or negative;
+    if !inValidInteger(result, ch) | ch != -1 | result < 0 then usage;
+
+    comment Output "prime" if number is prime, "composite" otherwise;
+    if isprime(result) then outstring(1, "prime")
+    else outstring(1, "composite")
+end