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https://github.com/kovidgoyal/kitty
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501f28acdf
* Switches to "positional notation" to fix the bug. * Consolidates `encode_hint` and `generate_prefix_free_hint` into `encode_hint`. * Moves prefix_free_hints.go to hints_generator.go; `encode_hint` and `decode_hint` were moved here too. * The "prefix-free" logic was made 0-index based instead of 1-index based for two reasons: 1. To simplify 1-off discrepancies. 2. To keep backwards compatibility with the old usage of `encode_hint`. * Slight perfomance improvement added by reusing the runt-to-index map instead of rebuilding for each call to `decode_hint`. * Unit tests added; for all new logic and old affected logic. Fixes #10231
91 lines
2.3 KiB
Go
91 lines
2.3 KiB
Go
// License: GPLv3 Copyright: 2026, Kovid Goyal, <kovid at kovidgoyal.net>
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package hints
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// hints_to_skip calculates how many hints to skip based on the given n and
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// alphabet size so that the next n hints generated by expanding the prefix tree
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// of an alphabet of size alphabetSize will be prefix-free.
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//
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// The result is 1-based, meaning that the first hint to be skipped is the first
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// non-empty hint.
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//
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// For example, if alphabet was "abc" and n was 5, the first non-empty hints
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// from that alphabet would be: "a", "b", "c", "aa", "ab", "ac", ...
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// the result of hints_to_skip would be 1, and this would mean that if you skip
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// "a" from the list above, the next 5 hints are prefix-free:
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// "b", "c", "aa", "ab", "ac".
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//
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// See issue #10195 for an informal proof on why this function works.
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func hints_to_skip(n int, alphabetSize int) int {
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if n < 2 {
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n = 2
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}
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return (n - 2) / (alphabetSize - 1)
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}
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// encode_hint generates the hint corresponding to the given index in the
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// breadth-first traversal of the prefix tree generated by the given alphabet.
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//
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// For example, given the alphabet "abc", the hints would be generated in
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// the following order:
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// 0. "a"
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// 1. "b"
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// 2. "c"
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// 3. "aa"
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// 4. "ab"
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// 5. "ac"
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// 6. "ba"
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// 7. "bb"
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// 8. "bc"
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// 9. "ca"
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// 10. "cb"
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// 11. "cc"
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// 12. "aaa"
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// ...
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//
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// Indices are 0-based on non-empty hints; index=0 the hint of length 1 with
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// the first character of the alphabet.
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func encode_hint(num int, alphabet string) (res string) {
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l := len(alphabet)
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for num >= 0 {
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mod := num % l
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res = string(alphabet[mod]) + res
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num /= l
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num -= 1
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}
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return
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}
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func rune_to_index_map(alphabet string) *map[rune]int {
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runeToIndexMap := make(map[rune]int)
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for index, char := range alphabet {
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runeToIndexMap[char] = index
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}
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return &runeToIndexMap
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}
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// decode_hint converts a hint to its corresponding index as it would appear in
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// the breadth-first traversal of the prefix tree generated by the given
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// alphabet.
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//
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// For example, given the alphabet "abc", the hints would be generated in
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// the following order:
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// 0. "a"
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// 1. "b"
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// 2. "c"
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// 3. "aa"
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// 4. "ab"
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// ...
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//
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// hint is expected to be non-empty.
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func decode_hint(hint string, char_to_index *map[rune]int) (res int) {
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base := len(*char_to_index)
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for _, c := range hint {
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res = res*base + ((*char_to_index)[c] + 1)
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}
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return res - 1
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}
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