[PD] floating-point question

[Mathieu Bouchard]

Le 2012-02-19 à 19:42:00, Jonathan Wilkes a écrit :

> With 64-bit floats does this problem practically go away (like getting 
> an index into a large table)?

Depends on how practical you need it to be.

32-bit floats have 23 explicit bits of numerator, and an implicit high bit 
that is always one. This causes the numerators to always be whole numbers 
picked between 16777216 and 33554431.

64-bit floats have 52 explicit bits of numerator, and an implicit high 
bit. This means 29 doublings of precision. Every error is 536870912 times 
smaller.

For indexing into a table, it's very hard to do something wrong using 
float64. For other things, ... you can always find something more picky 
about precision of floats, but they can get really hard to find as you 
increase precision.

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