std.math performance (SSE vs. real)

[Walter Bright via Digitalmars-d]

On 6/28/2014 2:47 AM, francesco cattoglio wrote:
> When you need accuracy, 999 times out of 1000 you change the numerical
> technique, you don't just blindly upgrade the precision.

I have experience doing numerical work? Upgrading the precision is the first 
thing people try.


> The only real reason one would use 80 bits is when there is an actual need of
> adding values which differ for more than 16 orders of magnitude. And I've never
> seen this happen in any numerical paper I've read.

It happens with both numerical integration and inverting matrices. Inverting 
matrices is commonplace for solving N equations with N unknowns.

Errors accumulate very rapidly and easily overwhelm the significance of the answer.


> Especially the numerical analysts themselves will pay that price. 64 bit HAS to
> be as fast as possible, if you want to be competitive when it comes to any kind
> of numerical work.

Getting the wrong answer quickly is not useful when you're calculating the 
stress levels in a part.

Again, I've done numerical programming in airframe design. The correct answer is 
what matters. You can accept wrong answers in graphics display algorithms, but 
not when designing critical parts.