commit 1418c8a5d49ecc38a20df07151a7fe942992aea4 (tree)
parent 10914dc31000bc5c3b7164a4101808719d3da07f
Author: Ryan Liptak <squeek502@hotmail.com>
Date: Sat, 13 Jul 2024 16:54:00 -0700
ArgIteratorWindows: Store last emitted code unit instead of checking the last 6 emitted bytes
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%
Diffstat:
| M | lib/std/process.zig | | | 94 | ++++++++++++++++++++++++++++++++++++++++++------------------------------------- |
1 file changed, 50 insertions(+), 44 deletions(-)
diff --git 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);
- }
-
- 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;
+ 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;
+
+ // 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);
},
}
}
