From 1418c8a5d49ecc38a20df07151a7fe942992aea4 Mon Sep 17 00:00:00 2001 From: Ryan Liptak Date: Sat, 13 Jul 2024 16:54:00 -0700 Subject: [PATCH] ArgIteratorWindows: Store last emitted code unit instead of checking the last 6 emitted bytes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Previously, to ensure args were encoded as well-formed WTF-8 (i.e. no encoded surrogate pairs), the code unit would be encoded and then the last 6 emitted bytes would be checked to see if they were a surrogate pair, and this was done for any emitted code unit (although this was not necessary, it should have only been done when emitting a low surrogate). After this commit, we still want to ensure well-formed WTF-8, but, to do so, the last emitted code point is stored, meaning we can just directly check that the last code unit is a high surrogate and the current code unit is a low surrogate to determine if we have a surrogate pair. This provides some performance benefit over and above a "use the same strategy as before but only check when we're emitting a low surrogate" implementation: Benchmark 1 (111 runs): benchargv-master.exe measurement mean ± σ min … max outliers delta wall_time 45.2ms ± 532us 44.5ms … 49.4ms 2 ( 2%) 0% peak_rss 6.49MB ± 3.94KB 6.46MB … 6.49MB 10 ( 9%) 0% Benchmark 2 (154 runs): benchargv-storelast.exe measurement mean ± σ min … max outliers delta wall_time 32.6ms ± 293us 32.2ms … 34.2ms 8 ( 5%) ⚡- 27.8% ± 0.2% peak_rss 6.49MB ± 5.15KB 6.46MB … 6.49MB 15 (10%) - 0.0% ± 0.0% Benchmark 3 (131 runs): benchargv-onlylow.exe measurement mean ± σ min … max outliers delta wall_time 38.4ms ± 257us 37.9ms … 39.6ms 5 ( 4%) ⚡- 15.1% ± 0.2% peak_rss 6.49MB ± 5.70KB 6.46MB … 6.49MB 9 ( 7%) - 0.0% ± 0.0% --- lib/std/process.zig | 92 ++++++++++++++++++++++++--------------------- 1 file changed, 49 insertions(+), 43 deletions(-) diff --git a/lib/std/process.zig b/lib/std/process.zig index 542376f580..be8576442d 100644 --- a/lib/std/process.zig +++ b/lib/std/process.zig @@ -717,14 +717,20 @@ pub const ArgIteratorWindows = struct { const eof = null; - fn emitBackslashes(self: *ArgIteratorWindows, count: usize) void { - for (0..count) |_| emitCharacter(self, '\\'); + /// Returns '\' if any backslashes are emitted, otherwise returns `last_emitted_code_unit`. + fn emitBackslashes(self: *ArgIteratorWindows, count: usize, last_emitted_code_unit: ?u16) ?u16 { + for (0..count) |_| { + self.buffer[self.end] = '\\'; + self.end += 1; + } + return if (count != 0) '\\' else last_emitted_code_unit; } - fn emitCharacter(self: *ArgIteratorWindows, code_unit: u16) void { - const wtf8_len = std.unicode.wtf8Encode(code_unit, self.buffer[self.end..]) catch unreachable; - self.end += wtf8_len; - + /// If `last_emitted_code_unit` and `code_unit` form a surrogate pair, then + /// the previously emitted high surrogate is overwritten by the codepoint encoded + /// by the surrogate pair, and `null` is returned. + /// Otherwise, `code_unit` is emitted and returned. + fn emitCharacter(self: *ArgIteratorWindows, code_unit: u16, last_emitted_code_unit: ?u16) ?u16 { // Because we are emitting WTF-8, we need to // check to see if we've emitted two consecutive surrogate // codepoints that form a valid surrogate pair in order @@ -745,28 +751,24 @@ pub const ArgIteratorWindows = struct { // and emit the codepoint it encodes, which in this // example is U+10437 (𐐷), which is encoded in UTF-8 as: // <0xF0><0x90><0x90><0xB7> - concatSurrogatePair(self); - } + if (last_emitted_code_unit != null and + std.unicode.utf16IsLowSurrogate(code_unit) and + std.unicode.utf16IsHighSurrogate(last_emitted_code_unit.?)) + { + const codepoint = std.unicode.utf16DecodeSurrogatePair(&.{ last_emitted_code_unit.?, code_unit }) catch unreachable; - fn concatSurrogatePair(self: *ArgIteratorWindows) void { - // Surrogate codepoints are always encoded as 3 bytes, so there - // must be 6 bytes for a surrogate pair to exist. - if (self.end - self.start >= 6) { - const window = self.buffer[self.end - 6 .. self.end]; - const view = unicode.Wtf8View.init(window) catch return; - var it = view.iterator(); - var pair: [2]u16 = undefined; - pair[0] = std.mem.nativeToLittle(u16, std.math.cast(u16, it.nextCodepoint().?) orelse return); - if (!unicode.utf16IsHighSurrogate(std.mem.littleToNative(u16, pair[0]))) return; - pair[1] = std.mem.nativeToLittle(u16, std.math.cast(u16, it.nextCodepoint().?) orelse return); - if (!unicode.utf16IsLowSurrogate(std.mem.littleToNative(u16, pair[1]))) return; - // We know we have a valid surrogate pair, so convert - // it to UTF-8, overwriting the surrogate pair's bytes - // and then chop off the extra bytes. - const len = unicode.utf16LeToUtf8(window, &pair) catch unreachable; - const delta = 6 - len; - self.end -= delta; + // Unpaired surrogate is 3 bytes long + const dest = self.buffer[self.end - 3 ..]; + const len = unicode.utf8Encode(codepoint, dest) catch unreachable; + // All codepoints that require a surrogate pair (> U+FFFF) are encoded as 4 bytes + assert(len == 4); + self.end += 1; + return null; } + + const wtf8_len = std.unicode.wtf8Encode(code_unit, self.buffer[self.end..]) catch unreachable; + self.end += wtf8_len; + return code_unit; } fn yieldArg(self: *ArgIteratorWindows) [:0]const u8 { @@ -783,9 +785,13 @@ pub const ArgIteratorWindows = struct { const eof = false; - fn emitBackslashes(_: *ArgIteratorWindows, _: usize) void {} + fn emitBackslashes(_: *ArgIteratorWindows, _: usize, last_emitted_code_unit: ?u16) ?u16 { + return last_emitted_code_unit; + } - fn emitCharacter(_: *ArgIteratorWindows, _: u16) void {} + fn emitCharacter(_: *ArgIteratorWindows, _: u16, last_emitted_code_unit: ?u16) ?u16 { + return last_emitted_code_unit; + } fn yieldArg(_: *ArgIteratorWindows) bool { return true; @@ -793,6 +799,7 @@ pub const ArgIteratorWindows = struct { }; fn nextWithStrategy(self: *ArgIteratorWindows, comptime strategy: type) strategy.T { + var last_emitted_code_unit: ?u16 = null; // The first argument (the executable name) uses different parsing rules. if (self.index == 0) { if (self.cmd_line.len == 0 or self.cmd_line[0] == 0) { @@ -815,15 +822,15 @@ pub const ArgIteratorWindows = struct { inside_quotes = !inside_quotes; }, ' ', '\t' => { - if (inside_quotes) - strategy.emitCharacter(self, char) - else { + if (inside_quotes) { + last_emitted_code_unit = strategy.emitCharacter(self, char, last_emitted_code_unit); + } else { self.index += 1; return strategy.yieldArg(self); } }, else => { - strategy.emitCharacter(self, char); + last_emitted_code_unit = strategy.emitCharacter(self, char, last_emitted_code_unit); }, } } @@ -861,29 +868,28 @@ pub const ArgIteratorWindows = struct { 0; switch (char) { 0 => { - strategy.emitBackslashes(self, backslash_count); + last_emitted_code_unit = strategy.emitBackslashes(self, backslash_count, last_emitted_code_unit); return strategy.yieldArg(self); }, ' ', '\t' => { - strategy.emitBackslashes(self, backslash_count); + last_emitted_code_unit = strategy.emitBackslashes(self, backslash_count, last_emitted_code_unit); backslash_count = 0; - if (inside_quotes) - strategy.emitCharacter(self, char) - else - return strategy.yieldArg(self); + if (inside_quotes) { + last_emitted_code_unit = strategy.emitCharacter(self, char, last_emitted_code_unit); + } else return strategy.yieldArg(self); }, '"' => { const char_is_escaped_quote = backslash_count % 2 != 0; - strategy.emitBackslashes(self, backslash_count / 2); + last_emitted_code_unit = strategy.emitBackslashes(self, backslash_count / 2, last_emitted_code_unit); backslash_count = 0; if (char_is_escaped_quote) { - strategy.emitCharacter(self, '"'); + last_emitted_code_unit = strategy.emitCharacter(self, '"', last_emitted_code_unit); } else { if (inside_quotes and self.index + 1 != self.cmd_line.len and mem.littleToNative(u16, self.cmd_line[self.index + 1]) == '"') { - strategy.emitCharacter(self, '"'); + last_emitted_code_unit = strategy.emitCharacter(self, '"', last_emitted_code_unit); self.index += 1; } else { inside_quotes = !inside_quotes; @@ -894,9 +900,9 @@ pub const ArgIteratorWindows = struct { backslash_count += 1; }, else => { - strategy.emitBackslashes(self, backslash_count); + last_emitted_code_unit = strategy.emitBackslashes(self, backslash_count, last_emitted_code_unit); backslash_count = 0; - strategy.emitCharacter(self, char); + last_emitted_code_unit = strategy.emitCharacter(self, char, last_emitted_code_unit); }, } }