> On Mar 30, 2017, at 8:10 PM, Greg Parker <gpar...@apple.com> wrote: > >> >> On Mar 30, 2017, at 7:09 PM, Carl Hoefs <newsli...@autonomy.caltech.edu >> <mailto:newsli...@autonomy.caltech.edu>> wrote: >> >> >>> On Mar 30, 2017, at 6:40 PM, Steve Bird <sb...@culverson.com >>> <mailto:sb...@culverson.com>> wrote: >>> >>> >>>> On Mar 30, 2017, at 8:25 PM, Carl Hoefs <newsli...@autonomy.caltech.edu >>>> <mailto:newsli...@autonomy.caltech.edu>> wrote: >>>> >>>> I have megabytes of raw legacy science datasets that I'm trying to read >>>> into my app and ingest into an array of doubles. The data is supposed to >>>> be organized as a stream of 8-byte doubles. I do not know how these >>>> datasets were generated, so I don't know what format (big/little endian, >>>> byte swapped, etc) they are in. >>>> Here is a hex dump of 4 binary doubles: >>>> >>>> 49BF7DE372533C05 A8C02FE3135B4F09 86C22FE37E630B05 27C2C4E3E258BA08 >>> >>> A few minutes of LabVIEW work shows some semi-reasonable values if you swap >>> bytes: >>> BF49E37D5372053C = -0.000790058 >>> C0A8E32F5B13094F = -3185.59 >>> >>> Do you know that those values are wrong? >> >> Hmm, the -3185.59 doesn't look right. The data is _supposed_ to be: >> >> 1st double: Time value, monotonically increasing, usually starting near >> 0.00000 >> 2nd double: Sensor value, oscillating waveform, centered about some >> arbitrary value >> >> So I'm expecting data like: >> >> 0.011 0.57525634765625 >> 0.012 0.45166015625000 >> 0.013 0.29907226562500 >> 0.014 0.13275146484375 >> 0.015 -0.03173828125000 >> 0.016 -0.18218994140625 >> 0.017 -0.29602050781250 >> 0.018 -0.38055419921875 >> ...etc. >> >> or even: >> >> 0.018 2089.66467285156250 >> 0.020 2087.57525634765625 >> 0.022 2085.45166015625000 >> 0.024 2083.29907226562500 >> 0.026 2082.13275146484375 >> 0.028 2081.03173828125000 >> 0.030 2080.18218994140625 >> 0.032 2080.29602050781250 >> 0.034 2079.38055419921875 >> 0.036 2079.43060302734375 >> 0.038 2078.44738769531250 >> 0.040 2076.43640136718750 >> ...etc >> >> When I manually swap the bytes in my program, I still end up with invalid >> values. >> -Carl >> >> 26 C3 E9 E2 6C 6A 38 0C 46 C3 E9 E2 6C 6A 40 0B 46 C3 E9 E2 83 6A DC 0A 66 >> C3 E9 E2 83 6A 0E 0B >> A5 C3 EF E2 AF 6A 40 0B A5 C3 EF E2 C6 6A 40 0B C5 C3 F5 E2 C6 6A 16 0A C5 >> C3 F5 E2 DC 6A 0E 0B >> 26 C3 3C E3 9E 62 B2 09 26 C3 3C E3 9E 62 B2 09 26 C3 36 E3 B4 62 BA 08 06 >> C3 36 E3 CB 62 C2 07 >> 45 C4 76 E3 44 6C 38 0C 25 C4 76 E3 5A 6C 06 0C 25 C4 76 E3 5A 6C DC 0A 05 >> C4 7D E3 70 6C DC 0A > > > Byte-swapped VAX type D might be right, but it's so easy to be off by a > factor of 2 here that it's hard to trust any guess. > > Using CFSwapInt64() from CoreFoundation/CFByteOrder.h and from_vax_d8() from > https://pubs.usgs.gov/of/2005/1424/ <https://pubs.usgs.gov/of/2005/1424/>, > your bytes above are: > -41.7215935353 > -49.7215935353 > -49.7215935353 > -49.7215935366 > -49.7215935366 > -57.7215935366 > -57.7215935366 > -82.9432328547 > -82.9432328547 > -82.9432328574 > -82.9432328574 > -98.9432786338 > -98.9432786338 > -98.9432786363 > -98.9432786363 > -41.7219100388 >
Enticing results! When I use CFSwapInt64(), it does this to the bytes: - raw bytes: 69BF5DE3 9F530306 - swp bytes: 0603539F E35DBF69 * [04] time_base: 2400969845129752384725738662412037010364031309686872696685853017835577483033453697155629104443247189829603912142488904070729903714756009814926441089319983058422454699494905107871645497808138444180815872.000000 The 'time_base' value is what I get when I printf the swapped-bytes value with a %f formatter. Not sure why you're getting good results... -Carl _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
