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Stop using LinearFifo in BufferedWriter

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Looking at the BufferedWriter assembly generated, one can see that is
has to do a lot of work, just to copy over some bytes and increase an
offset. This is because the LinearFifo is a much more general construct
than what BufferedWriter needs and the optimizer cannot prove that we
don't need to do this extra work.
This commit is contained in:
Jimmi Holst Christensen 2022-01-22 13:24:09 +01:00 committed by Andrew Kelley
parent fa84625aeb
commit 7287c7482a
1 changed files with 12 additions and 11 deletions
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23
lib/std/io/buffered_writer.zig
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@ -1,24 +1,22 @@
const std = @import("../std.zig");
const io = std.io;
const mem = std.mem;
pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) type {
return struct {
unbuffered_writer: WriterType,
fifo: FifoType = FifoType.init(),
buf: [buffer_size]u8 = undefined,
end: usize = 0,
pub const Error = WriterType.Error;
pub const Writer = io.Writer(*Self, Error, write);
const Self = @This();
const FifoType = std.fifo.LinearFifo(u8, std.fifo.LinearFifoBufferType{ .Static = buffer_size });
pub fn flush(self: *Self) !void {
while (true) {
const slice = self.fifo.readableSlice(0);
if (slice.len == 0) break;
try self.unbuffered_writer.writeAll(slice);
self.fifo.discard(slice.len);
}
try self.unbuffered_writer.writeAll(self.buf[0..self.end]);
self.end = 0;
}
pub fn writer(self: *Self) Writer {
@ -26,11 +24,14 @@ pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) ty
}
pub fn write(self: *Self, bytes: []const u8) Error!usize {
if (bytes.len >= self.fifo.writableLength()) {
if (self.end + bytes.len > self.buf.len) {
try self.flush();
return self.unbuffered_writer.write(bytes);
if (bytes.len > self.buf.len)
return self.unbuffered_writer.write(bytes);
}
self.fifo.writeAssumeCapacity(bytes);
mem.copy(u8, self.buf[self.end..], bytes);
self.end += bytes.len;
return bytes.len;
}
};