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merge_string_list

flatr

Function merge_string_list 

Source 
pub fn merge_string_list<'a, V, B, F>(
    views: &'a [V],
    out: &mut B,
    get_list: F,
) -> usize
where
    B: Buffer,
    F: Fn(&'a V) -> ListView<'a, String>,
Expand description

Merge a List(String) field using two-pass block copying.

§Layout of a string list in the source buffer

[jump_0][jump_1]...[jump_n-1]   ← jump table: n × u32, each a forward offset
[len_0][bytes_0][len_1][bytes_1] ← string pool: length-prefixed UTF-8 blobs

The jump table and string pool are contiguous but at different addresses, and the jump values are position-relative — they must be recomputed when moved to the new buffer.

§Algorithm

Pass A — for each view, block-copy the string pool (everything from offset + n*4 to last_offset + 4 + last_string_len) as a single copy_from_slice. Records the destination base address (dest_pool_start) for each view so Pass B can compute the fixup delta.

Pass B — for each view, block-copy the jump table, then add a constant delta to every entry. The delta collapses to:

delta = dest_pool_start - out.head()

measured before subtracting the jump-table size. This works because both the per-entry movement (dest_h - src_h_entry) and the per-string movement (dest_pool - src_pool) are factored out identically across all entries in the same view.

§Returns

The slot of the length-prefix u32, or 0 if all views were empty.