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I'm not sure how this fares in reguard to speed, but it only uses 2-5 scalars, tries to avoid generating intermidiate lists, and modifies their arguments inplace.
```sub shrink {
my \$dbit = 0;
for (my \$sbit = 0; \$sbit < length(\$_[0]) * 8; \$sbit++) {
next if \$sbit % 8 == 7;
vec(\$_[0], \$dbit++, 1) = vec(\$_[0], \$sbit, 1);
}
my \$dlen = length(\$_[0]) * 7 / 8;
\$dlen++ unless \$dlen == int(\$dlen);
\$dlen = int(\$dlen);
my \$extra = length(\$_[0]) - \$dlen;
if (\$extra > 0) {
substr(\$_[0], \$dlen, \$extra, '');
}
for (my \$pbit = \$dbit; \$pbit < \$dlen * 8; \$pbit++) {
vec(\$_[0], \$pbit, 1) = 0;
}
}

sub grow {
my \$sbit = int(length(\$_[0]) * 8 / 7) * 7 - 1;
for (my \$dbit = int(length(\$_[0]) * 8 / 7) * 8 - 1; \$dbit >= 0; \$d
+bit--) {
vec(\$_[0], \$dbit, 1) = \$dbit % 8 == 7 ? 0 : vec(\$_[0], \$sbit--
+, 1);
}
}
I have the nagging fealing there is a better way to implement ceil (near the middle of shrink).
If padding the compressed string with 0 bits is not needed then the second for loop of shrink can be omitted to save (on average) 4 bits of time.

In reply to Re^3: Efficient 7bit compression by Ven'Tatsu
in thread Efficient 7bit compression by Limbic~Region

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