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Date: Wed, 29 Aug 2007 16:20:47 +0100
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To: Pierre <pierre.php@gmail.com>
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References: <46CDA789.3080109@googlemail.com> <fe05d1540708260141s62ed7a41j93acf9589bb9aa9@mail.gmail.com>
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Subject: Re: [PHP-DEV] Testing math functions
From: zoe.slattery@googlemail.com (Zoe Slattery)

Pierre wrote:
> On 8/23/07, Zoe Slattery <zoe.slattery@googlemail.com> wrote:
>   
>> Hi - I've writing a few tests for the math extension and have a question
>> about floating point precision.
>>
>> Here's a small example:
>>
>> --TEST--
>> Test return type and value for expected input sin()
>> --INI--
>> precision = 14
>> --FILE--
>> <?php
>>
>> $threesixty = pi() * 2.0;
>> echo "sin 360 = ";
>> var_dump(sin($threesixty));
>>
>> ?>
>> --EXPECT--
>> sin 360 = float(-2.4492127076448E-16)
>>
>> Is it right to test for an exact number in this way? I was slightly
>> suprised that I got the same number from Windows and Linux (maybe I
>> shouldn't be).
>>
>> If not, I could write the test above to check that sin 360 is zero
>> plus/minus some small number - but how small?
>>     
>
> It really depends on the architecture. Using a precision of 10 should
> put you on the safe side, at least for the common architecture (intel,
> amd and ppc).
>   
Yes - you are right thanks. I'm currently testing that the answer is 
within +/- 1.0E-10 of what I expect - that works on the processor 
architectures that I have access to. I guess I'll find out what happens 
on the others wheh I check the test cases in :-).
> --Pierre
>
>