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ceil() misbehaving

Chris_D_Mentes_001Chris_D_Mentes_001 Member, csevp Posts: 55 PRO
I'm trying to round up a value but:
1. ceil(1) or ceil(1,1) return 1 and roundToPrecision(2,0) returns 2 as expected.
2. ceil((2405mm-1200mm)/(1200mm+5mm),1) returns 2 ??
3. roundToPrecision((2405mm+5mm)/(1200mm+5mm),0) returns 3 ??
Please tell me what I am doing wrong here!

Best Answers

  • _anton_anton Member, Onshape Employees Posts: 271
    Answer ✓
    #2 is because ((2405mm-1200mm)/(1200mm+5mm) is equal to slightly more than 1 because of floating-point math, and the ceil(..., 1) rounds it up to the next multiple of 1, which is 2.

    For #3, I'm getting 2.
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,354
    Answer ✓
    Yes, everything is stored in meters.
    Senior Director, Technical Services, EMEAI

Answers

  • _anton_anton Member, Onshape Employees Posts: 271
    Answer ✓
    #2 is because ((2405mm-1200mm)/(1200mm+5mm) is equal to slightly more than 1 because of floating-point math, and the ceil(..., 1) rounds it up to the next multiple of 1, which is 2.

    For #3, I'm getting 2.
  • Chris_D_Mentes_001Chris_D_Mentes_001 Member, csevp Posts: 55 PRO
    Okay I think what really gets me is that adding 5mm to 1200mm is where the error begins. This seems like it shouldn't happen even with rounding error. From what I've seen onshape uses IEEE standard 64 bit floating arithmatic.

    According to this link https://www.h-schmidt.net/FloatConverter/IEEE754.html I can see that I shouldn't have errors unless rather then FS units storing values with units as milimeters it actually stores them as meters. In other words 1200mm in the value with units type map is stored as 1.200 and units is meter.

    This seems to be consistant as I've tested it with a couple FS scripts:
    annotation { "Feature Type Name" : "SUM Print" }
    export const PrintMe = defineFeature(function(context is Context, id is Id, definition is map)
        precondition
        {
            annotation { "Name" : "X" }
            isLength(definition.X, LENGTH_BOUNDS);
            
            annotation { "Name" : "Y" }
            isLength(definition.Y, LENGTH_BOUNDS);
        }
        {
            var X = definition.X;
            var Y = definition.Y;
            println(X+Y);
        });
    
    annotation { "Feature Type Name" : "ADDfix Print" }
    export const PrintMeADDfix = defineFeature(function(context is Context, id is Id, definition is map)
        precondition
        {
            annotation { "Name" : "X" }
            isLength(definition.X, LENGTH_BOUNDS);
            
            annotation { "Name" : "Y" }
            isLength(definition.Y, LENGTH_BOUNDS);
        }
        {
            var X = definition.X*1000;
            var Y = definition.Y*1000;
            println((X+Y)/1000);
        });
    
    /*
    results in:
    1.2049999999999998 meter
    1.205 meter
    when I enter 1200mm and 5mm as X and Y
    */
    
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,354
    Answer ✓
    Yes, everything is stored in meters.
    Senior Director, Technical Services, EMEAI
  • Chris_D_Mentes_001Chris_D_Mentes_001 Member, csevp Posts: 55 PRO
    You're all beautiful people thank you!
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