• spir <denis.spir gmail.com> Feb 19 2011
• Simon Buerger <krox gmx.net> Feb 19 2011
• so <so so.so> Feb 21 2011

spir <denis.spir gmail.com> writes:

Hello,

What do you think of this?

unittest {
     assert(-1.1 + 2.2 == 1.1);          // pass
     assert(-1.1 + 2.2 + 3.3 == 4.4);    // pass
     assert(-1.1 + 3.3 + 2.2 == 4.4);    // fail
     assert(-1.1 + 3.3 == 2.2);          // fail
}

There is approxEquals in stdlib, right; but shouldn't builtin "==" be 
consistent anyway?

Denis
-- 
_________________
vita es estrany
spir.wikidot.com

Simon Buerger <krox gmx.net> writes:

On 19.02.2011 13:06, spir wrote:
 Hello,

 What do you think of this?

 unittest {
 assert(-1.1 + 2.2 == 1.1); // pass
 assert(-1.1 + 2.2 + 3.3 == 4.4); // pass
 assert(-1.1 + 3.3 + 2.2 == 4.4); // fail
 assert(-1.1 + 3.3 == 2.2); // fail
 }

 There is approxEquals in stdlib, right; but shouldn't builtin "==" be
 consistent anyway?

 Denis



It is generally a bad idea to use "==" with floats, as most decimals 
cant be represented exact in binary floating point. That means there 
is no float for the value "1.1". Though there are exact floats for 
0.25, 0.5, 42.125 and so on. The only reason the first two testcases 
work is, that it is rounded the same way both sides of the "==" but 
you should not rely on that.

Also note, that these calculations are probably done at compile-time, 
and the compiler is allowed to use a higher precision than at 
run-time, so you might get different result when you let the user 
input the numbers.

- Krox

so <so so.so> writes:

On Sat, 19 Feb 2011 14:06:38 +0200, spir <denis.spir gmail.com> wrote:

 Hello,

 What do you think of this?

 unittest {
      assert(-1.1 + 2.2 == 1.1);          // pass
      assert(-1.1 + 2.2 + 3.3 == 4.4);    // pass
      assert(-1.1 + 3.3 + 2.2 == 4.4);    // fail
      assert(-1.1 + 3.3 == 2.2);          // fail
 }

 There is approxEquals in stdlib, right; but shouldn't builtin "==" be  
 consistent anyway?

 Denis


Strange no one mentioned this.
Problem is not the floating point format in your example. I can do the  
same with integral numbers, how?

int(5) / int(2) => int(2) or int(3)? And why?
Answer depends on the rounding mode, if you don't know the given rounding  
mode for a (machine interpreted) number system you can't say anything.
You know the answer because you know the rule. I can say same for the  
floating points since i know how they work.