# Re: IEEE-754

*From*: Roman Töngi <roman.toengi@xxxxxxxxxx>*Date*: Thu, 23 Aug 2007 18:08:15 +0200

Boudewijn Dijkstra wrote:

Op Thu, 23 Aug 2007 12:45:52 +0200 schreef Roman Töngi <roman.toengi@xxxxxxxxxx>:From the IEEE-specification for double format.IEEE-754 Arithmetic:

Most real numbers can't be stored exactly on the computer, but there can

be stated the range within which a machine number lies.

For the following example, I assume double precision and the round mode in effect to be 'round to nearest' and that the number lies within the

normalized range:

Definitions:

x := real number

round(x) := correctly rounded normalized number

eps := machine epsilon (2^(-52) for double precision)

abs(x) := absolute value of x

That is:

round(x) = x*(1 + delta)

with delta:

abs(delta) <= 1/2*eps (round to nearest)

i.d. abs(delta) <= 2^(-53) (double precision)

abs(delta) corresponds to the relative rounding error.

Now I can state the range including round(x):

-----------------------------------------

x*(1-2(-53)) <= round(x) <= x*(1+2^(-53))

-----------------------------------------

Is this the correct range according to my assumptions?

Yes, but your assumptions are invalid. How did you arrive at a machine epsilon of 2^(-52)?

.

**Follow-Ups**:**Re: IEEE-754***From:*Boudewijn Dijkstra

**References**:**IEEE-754***From:*Roman Töngi

**Re: IEEE-754***From:*Boudewijn Dijkstra

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