Weird rounding issue

[Leanne]

It was my understanding that Miva uses bankers rounding, where numbers ending in 5 will round to the nearest even number. So, 0.125 rounds to 0.12 and 0.135 rounds to 0.14. However, I am not getting those rounding results.

    <mvt:assign name="g.discount_raw" value="109.25* .18" />
    <mvt:assign name="g.discount_rounded" value="rnd(g.discount_raw,2)" />
    <p>    
        $109.25 x .18 = &mvt:global:discount_raw; <br>
        &mvt:global:discount_raw rounded is &mvt:global:discount_rounded;
    </p>

Resulting output is consistent with bankers rounding:

$109.25 x .18 = 19.665
19.665 rounded is 19.66

    <mvt:assign name="g.discount_raw" value="84.75 * .18" />
    <mvt:assign name="g.discount_rounded" value="rnd(g.discount_raw,2)" />
    <p>    
        $84.75 x .18 = &mvt:global:discount_raw; <br>
        &mvt:global:discount_raw rounded is &mvt:global:discount_rounded;
    </p>

Resulting output is not consistent with bankers rounding (or at least not my understanding of it):

$84.75 x .18 = 15.255
15.255 rounded is 15.25

Is my understanding of Miva's rounding system incorrect? This makes it seem like numbers ending in 5 just round down?

[Bruce - PhosphorMedia]

I can't find it right now, but I believe there is a settings somewhere to use or not use 'Bankers' rounding. If that's not checked, it may effect what you are seeing.

[Leanne]

You are correct, there is, (under Store Settings, I believe) but it is specific to sales tax.

[Bruce - PhosphorMedia]

Yea, I don't think the general ROUND function uses bankers, that's why they had to add that to sales tax. Here's what they do in the sales tax module

<MvFUNCTION NAME = "StateTax_Round" PARAMETERS = "charge, round_meth" STANDARDOUTPUTLEVEL = "">
    <MvCOMMENT> Bankers' rounding: Round down on 4 or less, stay on 5, round up on 6 or more </MvCOMMENT>

    <MvIF EXPR = "{ l.round_meth EQ 'B' }">
        <MvFUNCTIONRETURN VALUE = "{ l.charge ROUND 2 }">
    </MvIF>

    <MvCOMMENT> Rounding up: Round up on 5 or more </MvCOMMENT>

    <MvASSIGN NAME = "l.pos" VALUE = "{ '.' IN l.charge }">

    <MvIF EXPR = "{ ( l.pos EQ 0 ) OR ( substring_var( l.charge, l.pos + 3, 1 ) NE '5' ) }">
        <MvFUNCTIONRETURN VALUE = "{ l.charge ROUND 2 }">
    </MvIF>

    <MvFUNCTIONRETURN VALUE = "{ ( l.charge + 0.001 ) ROUND 2 }">
</MvFUNCTION>

You'd have to adopt that to SMT code. (B is bankers :) )

[Leanne]

Thank you! This comment at the beginning of the code sample looks like it might explain my results. I'll do some more experimenting and see if that is actually what is happening.

 
 <MvCOMMENT> Bankers' rounding: Round down on 4 or less, stay on 5, round up on 6 or more </MvCOMMENT>

[Bruce - PhosphorMedia]

You can sometimes google math questions like this for a php based solution. Script Maths are pretty universal and relatively easy to convert.