Issue #22118 has been updated by matz (Yukihiro Matsumoto). I largely accept this proposal. Byte buffer manipulation is a real need, both for embedded Ruby and for CRuby where String already serves as the de facto byte container. Here are my decisions on the details. Naming: the vocabulary shall be `bit_get`, `bit_set`, `bit_clear`, `bit_flip`, `bit_count` (see #20163), and `bitwise_not/and/or/xor` with their `!` variants. The `bit_*` / `bitwise_*` distinction (single-bit inspection vs whole-buffer operation) is a good one. `bit_get` shall return `0 | 1 | nil`, consistent with `Integer#[]` and useful for arithmetic and copying bits between buffers. I understand the desire to write `if str.bit_get(index)`, but a boolean return would silently conflate a clear bit with an out-of-range offset, hiding off-by-one bugs. For the conditional use case, add a predicate `bit_set?(offset, ...)` returning `true`/`false` (`nil` for out of range); it pairs with the `bit_set` writer and matches Integer's bit predicates (`allbits?` etc.). `bit_set`/`bit_clear`/`bit_flip` being destructive-only is fine; a non-destructive variant that copies the whole buffer for one bit has little use, and `str.dup.bit_set(i)` is available. No `!` suffix, following the `setbyte` precedent: `!` marks the dangerous one of a pair, and there is no pair here. Please also specify the following explicitly in the ticket, not just in the PR: * Length mismatch in binary `bitwise_*` operations raises `ArgumentError`. Silent zero-extension would let corrupted results flow downstream in the typical use cases (checksums, masks); callers who want padding can `ljust` explicitly. * Encoding: the operations treat the receiver as bytes and the result encoding shall be specified (I suggest BINARY for non-destructive results). * The bit-order keyword must be accepted by all `bit_*` methods with the same default; a getter and a setter disagreeing on bit addressing would be disastrous. * Out-of-range offset: `bit_get` returns `nil` (like `getbyte`), the writers raise `IndexError` (like `setbyte`). Reads are lenient, writes are strict. Matz. ---------------------------------------- Feature #22118: Introduce Basic Bit Operations into String https://bugs.ruby-lang.org/issues/22118#change-118023 * Author: hasumikin (hitoshi hasumi) * Status: Open ---------------------------------------- This PR implements a subset of the specification proposed in the parent feature ticket #22082 PR URL: https://github.com/ruby/ruby/pull/17353 ## Methods implemented with the same specification as the parent ticket * `String#bit_at(offset, lsb_first: true) -> true | false | nil` * `String#bitwise_not -> String` * `String#bitwise_not! -> self` * `String#bitwise_and(other) -> String` * `String#bitwise_and!(other) -> self` * `String#bitwise_or(other) -> String` * `String#bitwise_or!(other) -> self` * `String#bitwise_xor(other) -> String` * `String#bitwise_xor!(other) -> self` ## Methods with range-oriented forms omitted for now The parent ticket also included range-oriented forms for some methods. In this PR, those range arguments are intentionally omitted, and the methods are limited to simpler forms. Range support can be considered as a future extension. * `String#bit_count -> Integer` * `String#bit_set(offset, lsb_first: true) -> self` * `String#bit_clear(offset, lsb_first: true) -> self` * `String#bit_flip(offset, lsb_first: true) -> self` In particular, `String#bit_count` currently takes no arguments. It does not accept a range, offset/length pair, or `lsb_first:` keyword. --- ## Remaining design questions even after narrowing the scope The overall direction of adding these methods has already been approved by Matz. The remaining questions are mostly about naming and API details. ### 1. Why the `bitwise_*` prefix is used In the parent ticket, all other methods are related to bit positions: they either take bit-position arguments, yield bit positions, or operate on a specified bit range. In contrast, the `bitwise_*` methods are whole-data operations. They apply to the entire string as a fixed-size bitmap and do not expose bit positions or bit ordering. The `bitwise_*` prefix is intended to make this distinction explicit. ### 2. Bit numbering #### `lsb_first: true` (default) Within each byte, `offset = 0` is the LSB. Numbering proceeds upward through byte[0] and then continues at the LSB of byte[1]: ```text byte[0] byte[1] offset: 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 bit: b7 b6 b5 b4 b3 b2 b1 b0 b7 b6 b5 b4 b3 b2 b1 b0 ^ ^ LSB LSB offset = byte_index * 8 + bit_in_byte ``` #### `lsb_first: false` for MSB-first Byte order is preserved (`byte[0]` is still first), but within each byte numbering starts at the MSB: ```text byte[0] byte[1] offset: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 bit: b7 b6 b5 b4 b3 b2 b1 b0 b7 b6 b5 b4 b3 b2 b1 b0 ^ ^ MSB MSB offset = byte_index * 8 + (7 - bit_in_byte) ``` * Whether `lsb_first:` is needed at all, or whether an equivalent mechanism should exist under another name? * If such a mechanism is needed, whether `lsb_first:` is the right keyword name? * If `lsb_first:` is acceptable, should its default be `true`? My point is that `lsb_first:` is needed because both bit numbering conventions are used in real byte-buffer formats. LSB-first is the more common convention for general in-memory bitmap use, including formats and APIs such as Apache Arrow validity bitmaps, ext4 block bitmaps, Roaring bitmaps, Linux/BSD bitmap APIs, and hardware register descriptions. MSB-first is also needed for domains such as RFC-style network protocol diagrams, PNG low-bit-depth scanlines, BitTorrent bitfields, and some compressed bit streams. The keyword only controls bit numbering within each byte. Byte order itself is unchanged. ### 3. Out-of-range behavior `String#bit_at` returns `nil` when the bit offset is out of range. On the other hand, mutating methods such as `String#bit_set`, `String#bit_clear`, and `String#bit_flip` raise `IndexError` for an out-of-range bit offset. This follows the same general distinction as read-like access versus write-like access: reading a missing position can return `nil`, but mutating a missing position should not silently do nothing. ### 4. Negative bit offsets Negative bit offsets are rejected with `IndexError`. Although Ruby often uses negative indices to count from the end, combining negative bit offsets with the `lsb_first: true/false` mechanism would make the numbering rule harder to explain and reason about. The API keeps bit offsets as non-negative flat positions from the beginning of the string. ### 5. Length mismatch for binary bitwise operations `String#bitwise_and`, `String#bitwise_or`, and `String#bitwise_xor` require both operands to have the same byte size. If the byte sizes differ, they raise `ArgumentError`. This avoids implicit truncation or zero-padding. Since these methods operate on strings as fixed-size bitmaps, requiring equal sizes makes the operation explicit and predictable. -- https://bugs.ruby-lang.org/