daylily
52 lines
1.6 KiB
Rust
52 lines
1.6 KiB
Rust
// 7-in-8 encoding. Each 7 bytes can be encoded into 8 bytes with all-0 MSB's. This is useful
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// for sending data over exotic protocols like MIDI SysEx.
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// Decode in-place, returning the decoded slice.
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pub fn decode_7in8(payload: &mut [u8]) -> &mut [u8] {
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let mut decoded_len = 0;
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for stride in 0..payload.len().div_ceil(8) {
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// Most significant bits of a 7-in-8 group
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let msbs = payload[8 * stride];
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for stroll in 1..8 {
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let in_ix = 8 * stride + stroll;
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if in_ix >= payload.len() {
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break;
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}
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payload[decoded_len] =
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(payload[in_ix] & 0b01111111) | ((msbs << (8 - stroll)) & 0b10000000);
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decoded_len += 1;
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}
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}
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&mut payload[..decoded_len]
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}
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// Encode into provided output buffer, returning the length of the output, or None if the buffer is too small.
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pub fn encode_7in8<'a>(payload: &[u8], output: &'a mut [u8]) -> Option<usize> {
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let mut encoded_len = 0;
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for stride in 0..payload.len().div_ceil(7) {
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let msbs_ix = encoded_len;
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if encoded_len >= output.len() {
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return None;
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}
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output[msbs_ix] = 0;
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encoded_len += 1;
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for stroll in 1..8 {
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let in_ix = 7 * stride + stroll - 1;
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if in_ix >= payload.len() {
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break;
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}
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if encoded_len >= output.len() {
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return None;
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}
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output[msbs_ix] |= (payload[in_ix] & 0b10000000) >> (8 - stroll);
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output[encoded_len] = payload[in_ix] & 0b01111111;
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encoded_len += 1;
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}
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}
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Some(encoded_len)
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}
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