Function encode_bits 

pub fn encode_bits(bits: usize, bytes: &[u8]) -> String

Encode a fixed number of bits (arbitrary length) as a Base44 string with optimal length.

This function treats the input bytes as a big integer containing exactly bits bits and encodes it using the minimum number of Base44 characters required.

Optimal Encoding

For N bits, the optimal Base44 length is ceil(N * log(2) / log(44)):

• 103 bits → 19 chars (2^103 < 44^19)
• 104 bits → 20 chars (2^104 < 44^20)
• 256 bits → 47 chars (2^256 < 44^47)

This is more efficient than byte-pair encoding when the bit count doesn’t align with byte boundaries, saving up to 5% space for certain bit lengths.

Performance Optimization

For small bit counts, native integer types are used for better performance:

• bits ≤ 64: uses u64 (fastest)
• bits ≤ 128: uses u128 (fast)
• bits > 128: uses BigUint (fallback)

Arguments

• bits - Number of significant bits (must be > 0). Bytes are read in little-endian order.
• bytes - Input bytes in LSB-first order (matching typical bit-packing schemes).

Example

// Encode 103 bits (13 bytes with top byte using 7 bits)
let data = [0u8; 13];
let encoded = qr_base44::encode_bits(103, &data);
assert_eq!(encoded.len(), 19); // Optimal length for 103 bits