Struct Wtf8Index 

pub struct Wtf8Index { /* private fields */ }

A code-point-index to byte-offset table for one WTF-8 buffer.

Implementations

impl Wtf8Index

pub fn new(data: &Wtf8, char_len: usize) -> Self

Builds the table for data, whose code point count is char_len.

O(data.len()), and touches every byte, so it pays for itself only when the caller goes on to index the buffer more than a couple of times.

pub fn byte_offset(&self, data: &Wtf8, index: usize) -> usize

The byte offset of data’s index-th code point.

data must be the buffer the table was built for, and index must be below its code point count.

pub fn char_index_at_byte( &self, data: &Wtf8, bytepos: usize, char_len: usize, ) -> usize

The index of the code point starting at byte offset bytepos, the inverse of Self::byte_offset.

data must be the buffer the table was built for, char_len its code point count, and bytepos a code point boundary at or before its end.

Logarithmic rather than constant: the table is keyed by code point index, so going the other way is a search through it. The bracketing below is what keeps that search short – a code point occupies one to four bytes, which pins the answer to a narrow band around bytepos before the first comparison.

pub fn byte_size(&self) -> usize

The table’s heap footprint, in bytes.