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DO NOT MERGE: bits pattern in unsafe_extract_byte regresses ~27x on native #4100

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DO NOT MERGE: bits pattern in unsafe_extract_byte regresses ~27x on native #4100

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8 changes: 2 additions & 6 deletions builtin/bitstring.mbt
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Original file line number Diff line number Diff line change
Expand Up @@ -83,9 +83,7 @@ pub fn ArrayView::unsafe_extract_byte(
(byte >> shift) & mask
} else {
// extract 16 bits at [byte_index, byte_index + 1]
let b0 = bs.unsafe_get(byte_index).to_uint()
let b1 = bs.unsafe_get(byte_index + 1).to_uint()
let data = (b0 << 8) | b1
guard! bs[byte_index:] is [u16be(data), ..]
// mask off the top bits

@bobzhang bobzhang Aug 19, 2026

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xx.get(i) is Some(y)
xx.get_view(i,j) is Some([i,j....]

let bit_mask = (1U << (16 - (offset & 7))) - 1
let data = data & bit_mask
Expand Down Expand Up @@ -959,9 +957,7 @@ pub fn BytesView::unsafe_extract_byte(
(byte >> shift) & mask
} else {
// extract 16 bits at [byte_index, byte_index + 1]
let b0 = bs.unsafe_get(byte_index).to_uint()
let b1 = bs.unsafe_get(byte_index + 1).to_uint()
let data = (b0 << 8) | b1
guard! bs[byte_index:] is [u16be(data), ..]
// mask off the top bits
let bit_mask = (1U << (16 - (offset & 7))) - 1
let data = data & bit_mask
Expand Down
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