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| cesar | lkcl: The RFP Overview page for project 2019-10-032 shows EUR 1250 budget left, while my pending RFP is for EUR 2500. I wonder if it's a problem? | 10:18 |
|---|---|---|
| lkcl | cesar, 1 sec let me check | 12:02 |
| lkcl | no it shouldn't be a problem | 12:03 |
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| lkcl | octavius, can you add dsld and dsrd to ls003? we cleared up the issue which was preventing them from being added | 13:13 |
| octavius | will do | 13:13 |
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| lkcl | i'm just editing the bigint page to add the pseudocode from the mdwn | 13:14 |
| lkcl | octavius, make sure to git pull, i just added pseudocode and also notes about adding VA2-Form | 13:31 |
| octavius | yep | 13:31 |
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| octavius | In the PowerISA spec, section 3.3.14.2.1 64-bit Fixed-Point Shift Instructions, is there a mistake? | 14:25 |
| octavius | sld pseudo-code says (RB)58:63, but the description says (RB)57:63 | 14:25 |
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| ghostmansd[m] | lkcl, thank you for changes with pattern | 15:32 |
| lkcl | really? in Power ISA v3.0B? | 15:36 |
| lkcl | yep that's a bug | 15:36 |
| lkcl | reporting it now | 15:40 |
| lkcl | ghostmansd[m], saves a lot of pissing about | 15:40 |
| ghostmansd[m] | This change should have had description "Improving UX in 3..2..1..." :-) | 15:41 |
| lkcl | mumble mumble... :) | 15:44 |
| programmerjake | octavius lkcl: sld pseudo-code says (RB)58:63 because it separately checks bit 57...so, no that is not a bug. | 17:55 |
| programmerjake | dsld/dsrd do not check bit 57 because that means we don't need an additional andi instruction when doing bigint shifts possibly by >64-bits | 17:57 |
| programmerjake | octavius lkcl: the MASK calls for dsld/dsrd should mirror sld/srd: sld: MASK(0, 63 - sh) srd: MASK(sh, 63) | 18:00 |
| programmerjake | also, why did you add setting overflow? dsld/dsrd do not set SO/OV | 18:01 |
| programmerjake | if any overflow-kinda thing is calculated, it should be like srad that sets CA iff the input is negative and 1-bits are shifted out to the right -- however, dsrd on a bigint can't keep track of the sign bit all the way to calculating the lsb word,so can't tell if the input bigint was negative -- therefore dsrd shouldn't detect overflow. dsld should mirror sld and never detect overflow. | 18:08 |
| programmerjake | sra[wd][i] setting CA is used to make right shift emulate a truncating division by a power of two, by incrementing the result using addze afterwards | 18:11 |
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| lkcl | okaay, lots of things to unpack. | 23:09 |
| lkcl | 1) checking bit 57 - thank you for spotting that. i closed the bugreport as invalid | 23:10 |
| lkcl | 2) when experimenting randomly to try to find something that passed a unit test, MASK(0, 63-sh) did not work (or, in my random hunting around i didn't find it) | 23:10 |
| lkcl | (yes, really, i can't do the analysis: i literally have to go through all permutations looking for "something that works") | 23:11 |
| lkcl | 3) i added overflow because it seemed like a good idea. ISACaller.handle_carry() will read *but not write* XER.SO - writing to XER.SO would only be permitted by a dsldo instruction (which is not worth it) | 23:14 |
| lkcl | the thought occurred to me it might be useful to have CR0.OV contain a notification as to whether the 64-bit carry was zero or nonzero | 23:15 |
| programmerjake | so you mean write OV but not SO? | 23:15 |
| lkcl | write CR0.OV bit, yes. write XER.SO, no | 23:15 |
| lkcl | see ISACaller.handle_comparison(). it *reads* XER.So and includes it (ORs in) in setting of CR0.SO | 23:16 |
| lkcl | it does *not* write to XER.SO (or any XER bits). | 23:16 |
| programmerjake | k, though i wasn't planning on writing CR0 at all | 23:16 |
| lkcl | that's only activated by OE=1 | 23:17 |
| lkcl | that's "dsld." and "dsrd." | 23:17 |
| programmerjake | ah, yeah | 23:17 |
| lkcl | which i just realised, in minor_4.csv, it's unnecessary to have CR0 as an output on this | 23:18 |
| lkcl | 10 52,SHIFT_ROT,OP_DSHL,RA,RB,RC,RT,NONE,CR0,0,0,ZERO,0,NONE,0,0,0,0,0,0,RC_ONLY,0 | 23:18 |
| lkcl | but... yeah it's ok "RC_ONLY" will detect it | 23:19 |
| lkcl | is it useful? honestly i don't know | 23:19 |
| lkcl | i can see the value of detecting if the last element had a "64-bit-carry". | 23:21 |
| lkcl | is it useful at all for prefix-codes, to know if the 64-bit-carry is non-zero? | 23:21 |
| lkcl | or when using this for grouping bits together (constructing an instruction from operand fields, for example) | 23:22 |
| programmerjake | yeah, it's useful for bigint as long as Rc is optional, allows saving an instruction to check for shift left overflowing (bigint needs one more word) or for signed shift right truncating instead of flooring for emulating division by a power of 2 | 23:23 |
| lkcl | yes it's optional. | 23:23 |
| programmerjake | Rc=0 should be an option to avoid overwriting CR predicates | 23:23 |
| lkcl | i have to say it feels slightly odd that these two are not natural inverses of each other | 23:23 |
| lkcl | yes agreed | 23:23 |
| lkcl | been thinking about that - using some of SVSTATE bits to change the offset where CR predicates start from | 23:24 |
| programmerjake | prefix-code doesn't care about non-zero outputs, after all codes that are a string of zeros are just as valid as strings of ones and need to be handled identically | 23:25 |
| lkcl | ahh | 23:25 |
| lkcl | https://git.libre-soc.org/?p=openpower-isa.git;a=commitdiff;h=a5e874ed4f20a8febed2f7cf51715e2a930f1f01 nice catch btw | 23:25 |
| programmerjake | imho using bits to expand offset for vslideup/vslidedown would be quite useful | 23:26 |
| lkcl | nggggh that one fell through the cracks | 23:26 |
| lkcl | have to think about it | 23:26 |
| lkcl | can you raise a bugreport and link it to... to... errr.. | 23:26 |
| lkcl | https://bugs.libre-soc.org/show_bug.cgi?id=952 | 23:27 |
| programmerjake | imho lots more of our ops likely don't calculate CA correctly because SelectableInt doesn't propagate carrys | 23:27 |
| programmerjake | uuh, already created a bug...https://bugs.libre-soc.org/show_bug.cgi?id=972 | 23:27 |
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| lkcl | awesome | 23:30 |
| lkcl | oh i meant for offsets | 23:31 |
| programmerjake | i'll make a bug for expanding svoffset | 23:32 |
| lkcl | magic | 23:32 |
| octavius | Have you prepared for the trip lkcl? You should get some good sleep before the drive :) | 23:35 |
| lkcl | sunday. yes. | 23:35 |
| octavius | Ah ok, plenty of time then | 23:36 |
| lkcl | peugeot's gearbox is f*****d - taking the toyota starlight instead | 23:36 |
| lkcl | ordered a replacement one with "only" 75,000 miles on it | 23:36 |
| octavius | Is it expensive to do the replacement? I guess such an old model has simpler disassembly | 23:37 |
| lkcl | god yes | 23:37 |
| lkcl | likely about GBP 350 quid in labour. | 23:37 |
| lkcl | 350 quid for the gearbox | 23:38 |
| octavius | :( | 23:38 |
| lkcl | there's is a certain appeal to a car this old - one that can run on vegetable oil straight into the tank and has no computer control whatsoever | 23:38 |
| octavius | No ECUs of anykind? | 23:39 |
| lkcl | looked it up: below 1250 litres per year, you do not need to pay tax | 23:39 |
| lkcl | nope. | 23:39 |
| lkcl | there's a cable. | 23:39 |
| lkcl | it goes to the throttle. | 23:39 |
| lkcl | it's got a screw-stop on it to limit how much "pull" the cable has. | 23:39 |
| octavius | Interesting, my car's 1.25l. But it's the age that makes it tax-exempt? | 23:40 |
| octavius | nice | 23:40 |
| lkcl | ah no - that's in 6 years time | 23:40 |
| lkcl | no, it's the UK Inland Revenue rules on "alternative fuels" | 23:40 |
| lkcl | https://www.gov.uk/guidance/biofuels-and-other-fuel-substitutes-excise-notice-179e-from-1-april-2022 | 23:41 |
| lkcl | 2500 litres, not 1250 | 23:41 |
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| lkcl | section 4.2.1 | 23:41 |
| lkcl | 2500 litres per year is 538 gallons. | 23:42 |
| lkcl | 538 gallons @ 60 mpg is over 32,000 miles :) | 23:42 |
| octavius | Ah, I thought of the engine volume...60mpg is very good! | 23:44 |
| lkcl | only 800 kg, that's why | 23:44 |
| octavius | Ah of course | 23:45 |
| octavius | My car is just under double that :D | 23:45 |
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