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ArgIteratorWindows: Store last emitted code unit instead of checking the last 6 emitted bytes

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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%
This commit is contained in:
Ryan Liptak 2024-07-13 16:54:00 -07:00
parent 10914dc310
commit 1418c8a5d4
1 changed files with 49 additions and 43 deletions
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92
lib/std/process.zig
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@ -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;
// 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;
}
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;
}
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);
},
}
}