Your terminology is very confusing, but it sounds to me like you want the numerical value 6416 aka 10010 from the string "64". For that, you can use hex.
$ perl -E'say 0x64 == hex("64") ?"yes":"no"'
yes
In case I misunderstood, here are some other related conversions:
numerical value 6416 from string "64" | hex("64")
| numerical value 6416 from string "100" | "100"
| packed byte 6416 from numerical value 6416 | chr(0x64)
| packed byte 6416 from string "64" | chr(hex("64"))
| packed byte 6416 from string "100" | chr("100")
| string "64" from numerical value 6416 | sprintf("%X", 0x64)
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pack 'C' would work in lieu of chr.
Update: I just noticed your followup. It seems that you want the packed byte 6416 (aka "d" in ASCII), but you didn't specify from what.
$ perl -E'say "\x64" eq chr(hex("64")) ?"yes":"no"'
yes
$ perl -E'say "\x64" eq chr(0x64) ?"yes":"no"'
yes
That could also be written
$ perl -E'say "\x64" eq pack("C", hex("64")) ?"yes":"no"'
yes
$ perl -E'say "\x64" eq pack("C", 0x64) ?"yes":"no"'
yes
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