[gstreamer-bugs] [Bug 342943] New: algorithm to avoid overflows when multiplying fractions

[GStreamer (bugzilla.gnome.org)]

Do not reply to this via email (we are currently unable to handle email
responses and they get discarded).  You can add comments to this bug at
http://bugzilla.gnome.org/show_bug.cgi?id=342943
 GStreamer | gstreamer (core) | Ver: HEAD CVS

           Summary: algorithm to avoid overflows when multiplying fractions
           Product: GStreamer
           Version: HEAD CVS
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: torri at iecn.u-nancy.fr
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


as requested by Thomas, i post here a simple algorithm that try to avoid some
overflows when multiplying fractions. It's only maths, no computer science.

To compute a fraction from a numerator num and a denominator den, first compute
the gcd d of num and den with the Euclid algorithm. Then the resulting
"simplified" fraction is (num / d, den / d).


if r1=(num1, den1) and r2=(num2, den2) are 2 fractions. I suppose that they are
already simplified.

a) compute the rational r3=(num1, den2) using the simplification above
b) compute the rational r4=(num2, den1) using the simplification above
c) the result of r1 * r2 is the rational r5=(r3.num * r4.num, r3.den * r4.den)
and it's no need to simplify this fraction. It's already simplified.

another way to say that : 

a) d1 = gcd(num1, den2)
b) d2 = gcd(num2, den1)
c) r1 * r2 is the fraction ( (num1 / d1) * (num2 / d2), (den1 / d2) * (den2 /
d1) )

they is another algo if the fraction is multiplied by an integer only.

I don't know if multiplications of fractions are handled this way in gstreamer.
Nevertheless, I hope this helps

Vincent


-- 
Configure bugmail: http://bugzilla.gnome.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the QA contact for the bug.
You are the assignee for the bug.