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<== Date ==> <== Thread ==>
Subject: Re: Store 64-bit integer in asyn parameter library?
From: Luca Cavalli <[email protected]>
To: Mark Rivers <[email protected]>, "J. Lewis Muir" <[email protected]>
Cc: EPICS Tech-Talk <[email protected]>
Date: Sat, 19 May 2018 07:14:17 +0000
Hi,

you can even provide both a string representation for GUI display and low and high parts as 32 bit integers for further processing (after 64 bit integer reconstruction by the consumer).

Ciao,

Luca


Da: J. Lewis Muir
Inviato: sabato 19 maggio, 00:21
Oggetto: Re: Store 64-bit integer in asyn parameter library?
A: Mark Rivers
Cc: EPICS Tech-Talk


On 05/18, Mark Rivers wrote: > This might actually be a good case to use a double. You get exact > representation for 52 bits, i.e. 20 bits more than int32, or 1M times > higher rate. Interesting. So that's for the IEEE 754 double-precision binary floating-point format (64-bit). Assuming epicsFloat64 is that, then the maximum integer, such that it and all smaller integers can be represented exactly, is 2^53 = 9,007,199,254,740,992 according to [1] and [2]. And I believe the minimum is just the negation of that since the sign has its own bit. I had to go read about the 64-bit format [3], and apparently there's one more bit available for the signficand, sometimes referred to as the hidden bit, which is where the 53 comes from (i.e., 52 + 1). The 64-bit format stores the number in binary normalized form, so the first bit will always be 1, so it is omitted, thus gaining one extra bit for the significand. Anyway, I guess I'll use asynParamFloat64, then, and return an error if the bit rate is less than -2^53 or greater than 2^53. Thanks! Lewis [1] https://stackoverflow.com/a/1848762 [2] https://stackoverflow.com/a/1848953 [3] https://en.wikipedia.org/wiki/IEEE_754-1985

 


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References:
Store 64-bit integer in asyn parameter library? J. Lewis Muir
Re: Store 64-bit integer in asyn parameter library? J. Lewis Muir
Re: Store 64-bit integer in asyn parameter library? Mark Rivers
Re: Store 64-bit integer in asyn parameter library? J. Lewis Muir
Re: Store 64-bit integer in asyn parameter library? Mark Rivers
Re: Store 64-bit integer in asyn parameter library? J. Lewis Muir
Re: Store 64-bit integer in asyn parameter library? Mark Rivers
Re: Store 64-bit integer in asyn parameter library? J. Lewis Muir
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