Convert 8 Byte timestamp to a human readable time!

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Art 2015-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/244731-convert-8-byte-timestamp-to-a-human-readable-time

评论： Art 2015-9-26

I created a Matlab script that reads a file and parses out data. One data field is 8 bytes and represents a timestamp in seconds.

I browsed around and asked a few questions and came up with the following code for reading the eight bytes and converting to a time in seconds: ("this_timestamp" is the full 8 bytes of time data, file is little-endian format)

message_timestamp = typecast(uint64(hex2dec([reshape(flipud(rot90(dec2hex(this_timestamp(8:-1:5)))),1,[]),reshape(flipud(rot90(dec2hex(this_timestamp(4:-1:1)))),1,[])])),'double');

This seems to work fine under most situations, (I get the times exactly as I know they should be), but in rare circumstances the times come out as "e-310". One case this happens in is when the 8 bytes are: "00 00 00 00 00 00 5d 40" which after converting should be 116.000000.

Is there something I'm doing (or not doing) that doesn't handle data with "0"s after the decimal?

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Answer 1

James Tursa 2015-9-23

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https://ww2.mathworks.cn/matlabcentral/answers/244731-convert-8-byte-timestamp-to-a-human-readable-time#answer_193511

编辑：James Tursa 2015-9-23

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I haven't gone through your one-liner in any detail, but if you are starting with the 8 bytes shown above, then a simple typecast seems to work on my PC (little endian):

>> h = ['00';'00';'00';'00';'00';'00';'5d';'40']  % the hex values
h =
00
00
00
00
00
00
5d
40
>> this_timestamp = uint8(hex2dec(h))  % the equivalent 8 bytes
this_timestamp =
    0
    0
    0
    0
    0
    0
   93
   64
>> typecast(this_timestamp,'double')
ans =
   116

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Art 2015-9-24

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Ahh! Although by accident, you pointed me in the right direction --> I am using dec2hex to create a single field of hex values that should be 8 digits long (4bytes). I needed to add ",2" to my dec2hex conversions to make sure every hex byte was 2 digits long. Otherwise the field was < 8 digits, missing some important zeros, and read as the wrong dec number. Should be:

message_timestamp = typecast(uint64(hex2dec([reshape(flipud(rot90(dec2hex(this_timestamp(8:-1:5) *,2*))),1,[]),reshape(flipud(rot90(dec2hex(this_timestamp(4:-1:1) *,2*))),1,[])])),'double');

Art 2015-9-26

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Also, thanks for pointing me to the much simpler solution. I was going through two steps too many. I was converting my dec to hex, and then back to dec when all I had to do was:

message_timestamp = typecast(uint8(this_timestamp(1:1:8)),'double');

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