[M3devel] LONGINT problem?

[Coleburn, Randy]

Ken:

On what platform (OS and CPU) are you building and running your Modula-3 program?

Support for LONGINT is a relatively new addition to CM3, so it is possible that something is broken.  Perhaps your program can help us track it down.

I haven't checked thru your program yet, but the fact that it gives the right answer using INTEGER, but not when using LONGINT, seems to point to the LONGINT implementation as a potential problem source we should investigate.

Regards,
Randy Coleburn

From: Ken Durocher [mailto:kcdurocher at gmail.com]
Sent: Thursday, July 14, 2011 7:00 PM
To: Jay K
Cc: m3devel
Subject: Re: [M3devel] LONGINT problem?

Sorry, to clarify, the LONGINT code does NOT give the correct output, but the INTEGER code DOES.

I did not write this C code, but it's output is the same as all the other examples (there is a Java example too, if you want that):

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

/* should be 64-bit integers if going over 1 billion */
typedef unsigned long xint;
#define FMT "%lu"

xint total, prim, max_peri;
xint U[][9] =  {{ 1, -2, 2,  2, -1, 2,  2, -2, 3},
                        { 1,  2, 2,  2,  1, 2,  2,  2, 3},
                        {-1,  2, 2, -2,  1, 2, -2,  2, 3}};

void new_tri(xint in[])
{
            int i;
            xint t[3], p = in[0] + in[1] + in[2];

            if (p > max_peri) return;

            prim ++;

            /* for every primitive triangle, its multiples would be right-angled too;
            * count them up to the max perimeter */
            total += max_peri / p;

            /* recursively produce next tier by multiplying the matrices */
            for (i = 0; i < 3; i++) {
                        t[0] = U[i][0] * in[0] + U[i][1] * in[1] + U[i][2] * in[2];
                        t[1] = U[i][3] * in[0] + U[i][4] * in[1] + U[i][5] * in[2];
                        t[2] = U[i][6] * in[0] + U[i][7] * in[1] + U[i][8] * in[2];
                        new_tri(t);
            }
}

int main()
{
            xint seed[3] = {3, 4, 5};

            for (max_peri = 10; max_peri <= 100000000; max_peri *= 10) {
                        total = prim = 0;
                        new_tri(seed);

                        printf(  "Up to "FMT": "FMT" triples, "FMT" primitives.\n",
                                    max_peri, total, prim);
            }
            return 0;
}

The output from that code is:

Up to 10: 0 triples, 0 primitives.
Up to 100: 17 triples, 7 primitives.
Up to 1000: 325 triples, 70 primitives.
Up to 10000: 4858 triples, 703 primitives.
Up to 100000: 64741 triples, 7026 primitives.
Up to 1000000: 808950 triples, 70229 primitives.
Up to 10000000: 9706567 triples, 702309 primitives.
Up to 100000000: 113236940 triples, 7023027 primitives.

Note this output corresponds with the INTEGER output.

On Thu, Jul 14, 2011 at 5:17 PM, Jay K <jay.krell at cornell.edu<mailto:jay.krell at cornell.edu>> wrote:
Can you isolate if the problem is the formating/printing, or if it is in the computation?
i.e.:

Use "unsafe" and print out a little hex dump of the integer/longint variables?

As well, what does LONGINT on a 64bit machine do? Eh..well, it might work, it might not.
Doesn't really matter. Let's focus on non-working 32bit machine with LONGINT.

Also, please confirm which is the right, i.e. by writing it in C.
Also, maybe just try to format as unsigned/hex using the safe interfaces?
Also, this will be good to add to our automated tests. Assuming it doesn't run too slowly.
Assuming it reproduces for anyone else (sorry, a bit rude of me).

Later, thank you,
 - Jay

________________________________
Date: Thu, 14 Jul 2011 16:26:05 -0500
From: kcdurocher at gmail.com<mailto:kcdurocher at gmail.com>
To: m3devel at elegosoft.com<mailto:m3devel at elegosoft.com>
Subject: [M3devel] LONGINT problem?


I was writing a program to calculate "Pythagorean triples" recursively, and ran into a problem.  Here's the program:

MODULE PyTriples EXPORTS Main;

IMPORT IO, Fmt;

VAR tcnt, pcnt, max, i: LONGINT;

PROCEDURE NewTriangle(a, b, c: LONGINT; VAR tcount, pcount: LONGINT) =
  VAR perim := a + b + c;
  BEGIN
    IF perim <= max THEN
      pcount := pcount + 1L;
      tcount := tcount + max DIV perim;
      NewTriangle(a-2L*b+2L*c, 2L*a-b+2L*c, 2L*a-2L*b+3L*c, tcount, pcount);
      NewTriangle(a+2L*b+2L*c, 2L*a+b+2L*c, 2L*a+2L*b+3L*c, tcount, pcount);
      NewTriangle(2L*b+2L*c-a, b+2L*c-2L*a, 2L*b+3L*c-2L*a, tcount, pcount);
    END;
  END NewTriangle;

BEGIN
i := 100L;

REPEAT
  max := i;
  tcnt := 0L;
  pcnt := 0L;
  NewTriangle(3L, 4L, 5L, tcnt, pcnt);
  IO.Put(Fmt.LongInt(i) & ": " & Fmt.LongInt(tcnt) & " Triples, " &
    Fmt.LongInt(pcnt) & " Primitives\n");
  i := i * 10L;
UNTIL i = 10000000L;

END PyTriples.

This outputs:

100: 17 Triples, 7 Primitives
1000: 325 Triples, 70 Primitives
10000: 0858 Triples, 703 Primitives
100000: 40701 Triples, 7024 Primitives
1000000: 808950 Triples, 70229 Primitives

However, if I just use INTEGER on a 64 bit machine, I get the proper output:

100: 17 Triples, 7 Primitives
1000: 325 Triples, 70 Primitives
10000: 4858 Triples, 703 Primitives
100000: 64741 Triples, 7026 Primitives
1000000: 808950 Triples, 70229 Primitives

Note how 10000 and 100000 are different. The code is literally exactly the same, only with LONGINT replaced by INTEGER.


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