with it, it's perl version dependent

If the output from pack 'd', ... on a earlier version of Perl, is the wrong endian for the need, it can be 'converted' by by applying reverse to the packed value:

c:\test>perl -E"say pack 'd<', 12345.67689" | od -t x1
0000000 7f de 54 a4 d6 1c c8 40 0d 0a
0000012

c:\test>perl -E"say pack 'd>', 12345.67689" | od -t x1
0000000 40 c8 1c d6 a4 54 de 7f 0d 0a
0000012

c:\test>perl -E"say pack 'd', 12345.67689" | od -t x1
0000000 7f de 54 a4 d6 1c c8 40 0d 0a
0000012

c:\test>perl -E"say scalar reverse pack 'd', 12345.67689" | od -t x1
0000000 40 c8 1c d6 a4 54 de 7f 0d 0a
0000012
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