Re: Making Lemonade (Floating-point format changes)

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Sujet : Re: Making Lemonade (Floating-point format changes)
De : cr88192 (at) *nospam* gmail.com (BGB)
Groupes : comp.arch
Date : 21. May 2024, 19:56:47
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <v2in93$n4pd$1@dont-email.me>
References : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
User-Agent : Mozilla Thunderbird
On 5/21/2024 12:17 PM, MitchAlsup1 wrote:
BGB wrote:
 
But OTOH, if 1.0+2.0 gives 2.999999, that is, not good enough, so there
>
is a lower limit here.
 1.0 has a fraction of 0
2.0 has a fraction of 0
1.0+2.0 has a fraction with a single HOB set.
all 3 above examples have the hidden bit set.
 Any implementation purporting to be IEEE 754 better not give anything
other than 3.0 !!
 
This is kinda the point.
But, then I realized, probably should have also included:
   5.0-2.0 should also give exactly 3.0
   2.0-5.0 should also give exactly -3.0
   ...
As the issue that can cause this is more common with subtraction (say, if one tries to cut corners by using bitwise inversion for negation and also not bothering with a carry in for the internal adder, ...).
Granted, this does add the cost that one effectively needs to do two copies of the adder, one computing the normal result, and the other a negated result (trying to do a negate after the fact having a much higher latency cost, vs doing both and then selecting which is needed).

Bad example. Even IBM and CRAY arithmetics, with all their problems,
were
not that bad.
There are ways to make the FPU that bad, but as I see it, this is below a minimum limit of acceptability.
Also, both Quake and typical JavaScript interpreters will lose their crap if this sort of thing happens (as in both cases, they may represent bit-flags in floating point numbers and set/clear them with FADD/FSUB, which while questionable, does effectively set a minimum requirement for this...).

Date Sujet#  Auteur
12 May 24 * Making Lemonade (Floating-point format changes)101John Savard
12 May 24 +* Re: Making Lemonade (Floating-point format changes)3wolfgang kern
15 May 24 i`* Re: Making Lemonade (Floating-point format changes)2Michael S
15 May 24 i `- Re: Making Lemonade (Floating-point format changes)1BGB
12 May 24 +* Re: Making Lemonade (Floating-point format changes)6Thomas Koenig
12 May 24 i`* Re: Making Lemonade (Floating-point format changes)5John Savard
12 May 24 i +- Re: Making Lemonade (Floating-point format changes)1John Savard
12 May 24 i `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
13 May 24 i  `* Re: Making Lemonade (Floating-point format changes)2John Savard
13 May 24 i   `- Re: Making Lemonade (Floating-point format changes)1BGB
12 May 24 `* Re: Making Lemonade (Floating-point format changes)91John Dallman
12 May 24  `* Re: Making Lemonade (Floating-point format changes)90Thomas Koenig
13 May 24   `* Re: Making Lemonade (Floating-point format changes)89Michael S
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14 May 24    i`* Re: Making Lemonade (Floating-point format changes)55Michael S
15 May 24    i `* Re: Making Lemonade (Floating-point format changes)54Thomas Koenig
15 May 24    i  `* Re: Making Lemonade (Floating-point format changes)53Michael S
19 May 24    i   `* Re: Making Lemonade (Floating-point format changes)52Thomas Koenig
19 May 24    i    +* Re: Making Lemonade (Floating-point format changes)3Michael S
19 May 24    i    i+- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
20 May 24    i    i`- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
19 May 24    i    `* Re: Making Lemonade (Floating-point format changes)48Terje Mathisen
19 May 24    i     +* Re: Making Lemonade (Floating-point format changes)40Michael S
19 May 24    i     i+- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
20 May 24    i     i+* Re: Making Lemonade (Floating-point format changes)30Terje Mathisen
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20 May 24    i     ii `* Re: Making Lemonade (Floating-point format changes)28Terje Mathisen
20 May 24    i     ii  `* Re: Making Lemonade (Floating-point format changes)27Michael S
20 May 24    i     ii   +* Re: Making Lemonade (Floating-point format changes)19BGB
20 May 24    i     ii   i`* Re: Making Lemonade (Floating-point format changes)18MitchAlsup1
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20 May 24    i     ii   i +- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
21 May 24    i     ii   i `* Re: Making Lemonade (Floating-point format changes)15BGB
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22 May 24    i     ii   i  iii  `- Re: Making Lemonade (Floating-point format changes)1BGB-Alt
21 May 24    i     ii   i  ii`- Re: Making Lemonade (Floating-point format changes)1Thomas Koenig
21 May 24    i     ii   i  i`* Re: Making Lemonade (Floating-point format changes)4BGB
21 May 24    i     ii   i  i `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
21 May 24    i     ii   i  i  +- Re: Making Lemonade (Floating-point format changes)1BGB
22 May 24    i     ii   i  i  `- Re: Making Lemonade (Floating-point format changes)1Terje Mathisen
21 May 24    i     ii   i  `* Re: Making Lemonade (Floating-point format changes)2MitchAlsup1
21 May 24    i     ii   i   `- Re: Making Lemonade (Floating-point format changes)1BGB
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21 May 24    i     ii     `* Re: Making Lemonade (Floating-point format changes)5MitchAlsup1
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22 May 24    i     ii      `- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
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25 May 24    i     i      `* Re: binary128 implementation2MitchAlsup1
25 May 24    i     i       `- Re: binary128 implementation1BGB
19 May 24    i     +* Re: Making Lemonade (Floating-point format changes)6BGB
19 May 24    i     i`* Re: Making Lemonade (Floating-point format changes)5MitchAlsup1
20 May 24    i     i `* Re: Making Lemonade (Floating-point format changes)4BGB
20 May 24    i     i  `* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
20 May 24    i     i   `* Re: Making Lemonade (Floating-point format changes)2BGB
20 May 24    i     i    `- Re: Making Lemonade (Floating-point format changes)1MitchAlsup1
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13 May 24     `* Re: Making Lemonade (Floating-point format changes)31MitchAlsup1
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14 May 24      i `* Re: Making Lemonade (Floating-point format changes)20BGB
14 May 24      i  `* Re: Making Lemonade (Floating-point format changes)19MitchAlsup1
14 May 24      i   +* Re: Making Lemonade (Floating-point format changes)2Michael S
15 May 24      i   i`- Re: Making Lemonade (Floating-point format changes)1Michael S
14 May 24      i   +- Re: Making Lemonade (Floating-point format changes)1BGB
16 May 24      i   `* Re: Making Lemonade (Floating-point format changes)15MitchAlsup1
17 May 24      i    `* Re: Making Lemonade (Floating-point format changes)14MitchAlsup1
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19 May 24      i        `* Re: Making Lemonade (Floating-point format changes)8Chris M. Thomasson
20 May 24      i         `* Re: Making Lemonade (Floating-point format changes)7Chris M. Thomasson
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14 May 24      i`* Re: Making Lemonade (Floating-point format changes)3MitchAlsup1
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14 May 24      i `- Re: Making Lemonade (Floating-point format changes)1BGB
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