If anyone else is still reading at this point, and wants to check my working, I think I've demonstrated clearly that this is not a reversible compression scheme.
The two letter word "Pi" gives an index of 148.
The following 156 two letter words also give the same index:
(This is restricted to just printable characters, there could be far more matches using the full 256 combinations for each byte)
String: 0i (0011000001101001) Index: 148
String: 0j (0011000001101010) Index: 148
String: 0l (0011000001101100) Index: 148
String: 1I (0011000101001001) Index: 148
String: 1J (0011000101001010) Index: 148
String: 1L (0011000101001100) Index: 148
String: 8I (0011100001001001) Index: 148
String: 8J (0011100001001010) Index: 148
String: 8L (0011100001001100) Index: 148
String: 9A (0011100101000001) Index: 148
String: 9B (0011100101000010) Index: 148
String: 9D (0011100101000100) Index: 148
String: :A (0011101001000001) Index: 148
String: :B (0011101001000010) Index: 148
String:
(0011101001000100) Index: 148
String: <A (0011110001000001) Index: 148
String: <B (0011110001000010) Index: 148
String: <D (0011110001000100) Index: 148
String: @; (0100000000111011) Index: 148
String: @= (0100000000111101) Index: 148
String: @> (0100000000111110) Index: 148
String: @[ (0100000001011011) Index: 148
String: @] (0100000001011101) Index: 148
String: @^ (0100000001011110) Index: 148
String: @k (0100000001101011) Index: 148
String: @m (0100000001101101) Index: 148
String: @n (0100000001101110) Index: 148
String: @y (0100000001111001) Index: 148
String: A9 (0100000100111001) Index: 148
String: A: (0100000100111010) Index: 148
String: A< (0100000100111100) Index: 148
String: AK (0100000101001011) Index: 148
String: AM (0100000101001101) Index: 148
String: AN (0100000101001110) Index: 148
String: AY (0100000101011001) Index: 148
String: AZ (0100000101011010) Index: 148
String: A\ (0100000101011100) Index: 148
String: Ai (0100000101101001) Index: 148
String: Aj (0100000101101010) Index: 148
String: Al (0100000101101100) Index: 148
String: B9 (0100001000111001) Index: 148
String: B: (0100001000111010) Index: 148
String: B< (0100001000111100) Index: 148
String: BK (0100001001001011) Index: 148
String: BM (0100001001001101) Index: 148
String: BN (0100001001001110) Index: 148
String: BY (0100001001011001) Index: 148
String: BZ (0100001001011010) Index: 148
String: B\ (0100001001011100) Index: 148
String: Bi (0100001001101001) Index: 148
String: Bj (0100001001101010) Index: 148
String: Bl (0100001001101100) Index: 148
String: CI (0100001101001001) Index: 148
String: CJ (0100001101001010) Index: 148
String: CL (0100001101001100) Index: 148
String: D9 (0100010000111001) Index: 148
String: D: (0100010000111010) Index: 148
String: D< (0100010000111100) Index: 148
String: DK (0100010001001011) Index: 148
String: DM (0100010001001101) Index: 148
String: DN (0100010001001110) Index: 148
String: DY (0100010001011001) Index: 148
String: DZ (0100010001011010) Index: 148
String: D\ (0100010001011100) Index: 148
String: Di (0100010001101001) Index: 148
String: Dj (0100010001101010) Index: 148
String: Dl (0100010001101100) Index: 148
String: EI (0100010101001001) Index: 148
String: EJ (0100010101001010) Index: 148
String: EL (0100010101001100) Index: 148
String: GA (0100011101000001) Index: 148
String: GB (0100011101000010) Index: 148
String: GD (0100011101000100) Index: 148
String: H9 (0100100000111001) Index: 148
String: H: (0100100000111010) Index: 148
String: H< (0100100000111100) Index: 148
String: HK (0100100001001011) Index: 148
String: HM (0100100001001101) Index: 148
String: HN (0100100001001110) Index: 148
String: HY (0100100001011001) Index: 148
String: HZ (0100100001011010) Index: 148
String: H\ (0100100001011100) Index: 148
String: Hi (0100100001101001) Index: 148
String: Hj (0100100001101010) Index: 148
String: Hl (0100100001101100) Index: 148
String: MA (0100110101000001) Index: 148
String: MB (0100110101000010) Index: 148
String: MD (0100110101000100) Index: 148
String: P9 (0101000000111001) Index: 148
String: P: (0101000000111010) Index: 148
String: P< (0101000000111100) Index: 148
String: PK (0101000001001011) Index: 148
String: PM (0101000001001101) Index: 148
String: PN (0101000001001110) Index: 148
String: PY (0101000001011001) Index: 148
String: PZ (0101000001011010) Index: 148
String: P\ (0101000001011100) Index: 148
String: Pi (0101000001101001) Index: 148
String: Pj (0101000001101010) Index: 148
String: Pl (0101000001101100) Index: 148
String: QI (0101000101001001) Index: 148
String: QJ (0101000101001010) Index: 148
String: QL (0101000101001100) Index: 148
String: SA (0101001101000001) Index: 148
String: SB (0101001101000010) Index: 148
String: SD (0101001101000100) Index: 148
String: UA (0101010101000001) Index: 148
String: UB (0101010101000010) Index: 148
String: UD (0101010101000100) Index: 148
String: YA (0101100101000001) Index: 148
String: YB (0101100101000010) Index: 148
String: YD (0101100101000100) Index: 148
String: ZA (0101101001000001) Index: 148
String: ZB (0101101001000010) Index: 148
String: ZD (0101101001000100) Index: 148
String: \A (0101110001000001) Index: 148
String: \B (0101110001000010) Index: 148
String: \D (0101110001000100) Index: 148
String: `9 (0110000000111001) Index: 148
String: `: (0110000000111010) Index: 148
String: `< (0110000000111100) Index: 148
String: `K (0110000001001011) Index: 148
String: `M (0110000001001101) Index: 148
String: `N (0110000001001110) Index: 148
String: `Y (0110000001011001) Index: 148
String: `Z (0110000001011010) Index: 148
String: `\ (0110000001011100) Index: 148
String: `i (0110000001101001) Index: 148
String: `j (0110000001101010) Index: 148
String: `l (0110000001101100) Index: 148
String: aI (0110000101001001) Index: 148
String: aJ (0110000101001010) Index: 148
String: aL (0110000101001100) Index: 148
String: cA (0110001101000001) Index: 148
String: cB (0110001101000010) Index: 148
String: cD (0110001101000100) Index: 148
String: eA (0110010101000001) Index: 148
String: eB (0110010101000010) Index: 148
String: eD (0110010101000100) Index: 148
String: iA (0110100101000001) Index: 148
String: iB (0110100101000010) Index: 148
String: iD (0110100101000100) Index: 148
String: jA (0110101001000001) Index: 148
String: jB (0110101001000010) Index: 148
String: jD (0110101001000100) Index: 148
String: lA (0110110001000001) Index: 148
String: lB (0110110001000010) Index: 148
String: lD (0110110001000100) Index: 148
String: qA (0111000101000001) Index: 148
String: qB (0111000101000010) Index: 148
String: qD (0111000101000100) Index: 148
String: rA (0111001001000001) Index: 148
String: rB (0111001001000010) Index: 148
String: rD (0111001001000100) Index: 148
String: tA (0111010001000001) Index: 148
String: tB (0111010001000010) Index: 148
String: tD (0111010001000100) Index: 148
In fact, even with the single character 'P', there are three other printable characters with the same index:
String: B (01000010) Index: 74
String: D (01000100) Index: 74
String: P (01010000) Index: 74
String: ` (01100000) Index: 74