Unfortunately, the bitpatterns you generate -- in common with those used by grimey's code -- are not compatible with vec.

By way of example, this generates a vector with a single length 1x0 run, and a single length 2x0 run; and single length 3x0 run; and so on:

$vec = ''; 
$n=-1; 
vec( $vec, $n+=$_, 1 ) = 1 for 2 .. 17; 
print unpack 'b*', $vec;;
0100100010000100000100000010000000100000000100000000010000000000100000
+000000100000000000010000000000000100000000000000100000000000000010000
+0000000000001000...
# 2  5   9    14    20     27      35       44        54         65   
+       77           90            104            119             135 
+             152
[download]

Thus, a search for

• 1 x 0 should be found at position 0;
• 2 x 0 should be found at position 2;
• 3@5; 4@9; 5@14; ...

Running your code looking for these runs against that vector produces:

wrog  1: 0
wrog  2: 14
wrog  3: 5
wrog  4: 14
wrog  5: 14
wrog  6: 20
wrog  7: 27
wrog  8: 35
wrog  9: 44
wrog  10: 54
wrog  11: 65
wrog  12: 77
wrog  13: 90
wrog  14: 90
wrog  15: 90
wrog  16: 90
wrog  17: 90
[download]

I believe this is because little-endian bytes are bytes swapped and word swapped relative to big-endian.