From 6c7da0b526959840240177c0defb680e76fecad6 Mon Sep 17 00:00:00 2001 From: Jose Colon Rodriguez Date: Sun, 18 Feb 2024 11:14:43 -0400 Subject: Testing Ghostty's Utf8Decoder. A bit slower --- src/Utf8Decoder.zig | 142 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 src/Utf8Decoder.zig (limited to 'src/Utf8Decoder.zig') diff --git a/src/Utf8Decoder.zig b/src/Utf8Decoder.zig new file mode 100644 index 0000000..6bb0d98 --- /dev/null +++ b/src/Utf8Decoder.zig @@ -0,0 +1,142 @@ +//! DFA-based non-allocating error-replacing UTF-8 decoder. +//! +//! This implementation is based largely on the excellent work of +//! Bjoern Hoehrmann, with slight modifications to support error- +//! replacement. +//! +//! For details on Bjoern's DFA-based UTF-8 decoder, see +//! http://bjoern.hoehrmann.de/utf-8/decoder/dfa (MIT licensed) +const UTF8Decoder = @This(); + +const std = @import("std"); +const testing = std.testing; + +const log = std.log.scoped(.utf8decoder); + +// zig fmt: off +const char_classes = [_]u4{ + 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, + 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, + 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, + 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, + 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, 9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, + 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, 7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, + 8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2, 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, + 10,3,3,3,3,3,3,3,3,3,3,3,3,4,3,3, 11,6,6,6,5,8,8,8,8,8,8,8,8,8,8,8, +}; + +const transitions = [_]u8 { + 0,12,24,36,60,96,84,12,12,12,48,72, 12,12,12,12,12,12,12,12,12,12,12,12, + 12, 0,12,12,12,12,12, 0,12, 0,12,12, 12,24,12,12,12,12,12,24,12,24,12,12, + 12,12,12,12,12,12,12,24,12,12,12,12, 12,24,12,12,12,12,12,12,12,24,12,12, + 12,12,12,12,12,12,12,36,12,36,12,12, 12,36,12,12,12,12,12,36,12,36,12,12, + 12,36,12,12,12,12,12,12,12,12,12,12, +}; +// zig fmt: on + +// DFA states +const ACCEPT_STATE = 0; +const REJECT_STATE = 12; + +// This is where we accumulate our current codepoint. +accumulator: u21 = 0, +// The internal state of the DFA. +state: u8 = ACCEPT_STATE, + +/// Takes the next byte in the utf-8 sequence and emits a tuple of +/// - The codepoint that was generated, if there is one. +/// - A boolean that indicates whether the provided byte was consumed. +/// +/// The only case where the byte is not consumed is if an ill-formed +/// sequence is reached, in which case a replacement character will be +/// emitted and the byte will not be consumed. +/// +/// If the byte is not consumed, the caller is responsible for calling +/// again with the same byte before continuing. +pub inline fn next(self: *UTF8Decoder, byte: u8) struct { ?u21, bool } { + const char_class = char_classes[byte]; + + const initial_state = self.state; + + if (self.state != ACCEPT_STATE) { + self.accumulator <<= 6; + self.accumulator |= (byte & 0x3F); + } else { + self.accumulator = (@as(u21, 0xFF) >> char_class) & (byte); + } + + self.state = transitions[self.state + char_class]; + + if (self.state == ACCEPT_STATE) { + defer self.accumulator = 0; + + // Emit the fully decoded codepoint. + return .{ self.accumulator, true }; + } else if (self.state == REJECT_STATE) { + self.accumulator = 0; + self.state = ACCEPT_STATE; + // Emit a replacement character. If we rejected the first byte + // in a sequence, then it was consumed, otherwise it was not. + return .{ 0xFFFD, initial_state == ACCEPT_STATE }; + } else { + // Emit nothing, we're in the middle of a sequence. + return .{ null, true }; + } +} + +test "ASCII" { + var d: UTF8Decoder = .{}; + var out: [13]u8 = undefined; + for ("Hello, World!", 0..) |byte, i| { + const res = d.next(byte); + try testing.expect(res[1]); + if (res[0]) |codepoint| { + out[i] = @intCast(codepoint); + } + } + + try testing.expect(std.mem.eql(u8, &out, "Hello, World!")); +} + +test "Well formed utf-8" { + var d: UTF8Decoder = .{}; + var out: [4]u21 = undefined; + var i: usize = 0; + // 4 bytes, 3 bytes, 2 bytes, 1 byte + for ("๐Ÿ˜„โœครA") |byte| { + var consumed = false; + while (!consumed) { + const res = d.next(byte); + consumed = res[1]; + // There are no errors in this sequence, so + // every byte should be consumed first try. + try testing.expect(consumed == true); + if (res[0]) |codepoint| { + out[i] = codepoint; + i += 1; + } + } + } + + try testing.expect(std.mem.eql(u21, &out, &[_]u21{ 0x1F604, 0x2724, 0xC1, 0x41 })); +} + +test "Partially invalid utf-8" { + var d: UTF8Decoder = .{}; + var out: [5]u21 = undefined; + var i: usize = 0; + // Illegally terminated sequence, valid sequence, illegal surrogate pair. + for ("\xF0\x9F๐Ÿ˜„\xED\xA0\x80") |byte| { + var consumed = false; + while (!consumed) { + const res = d.next(byte); + consumed = res[1]; + if (res[0]) |codepoint| { + out[i] = codepoint; + i += 1; + } + } + } + + try testing.expect(std.mem.eql(u21, &out, &[_]u21{ 0xFFFD, 0x1F604, 0xFFFD, 0xFFFD, 0xFFFD })); +} -- cgit v1.2.3