authorgravatar for jhc@dismail.deJimmi Holst Christensen <jhc@dismail.de> 2022-01-22 13:24:09+01:00
committergravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2022-01-23 14:41:15-05:00
log7287c7482a2c694c7c7f56b9f7c1744a7ae7905f
tree9a8a3ace5afc9d45a17b9e07f6d1bdf3055e2a78
parentfa84625aeb852cc921cb596f4baccd452c3ce3b6

Stop using LinearFifo in BufferedWriter

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.

1 files changed, 12 insertions(+), 11 deletions(-)

lib/std/io/buffered_writer.zig+12-11
...@@ -1,24 +1,22 @@...@@ -1,24 +1,22 @@
1const std = @import("../std.zig");1const std = @import("../std.zig");
2
2const io = std.io;3const io = std.io;
4const mem = std.mem;
35
4pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) type {6pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) type {
5 return struct {7 return struct {
6 unbuffered_writer: WriterType,8 unbuffered_writer: WriterType,
7 fifo: FifoType = FifoType.init(),9 buf: [buffer_size]u8 = undefined,
10 end: usize = 0,
811
9 pub const Error = WriterType.Error;12 pub const Error = WriterType.Error;
10 pub const Writer = io.Writer(*Self, Error, write);13 pub const Writer = io.Writer(*Self, Error, write);
1114
12 const Self = @This();15 const Self = @This();
13 const FifoType = std.fifo.LinearFifo(u8, std.fifo.LinearFifoBufferType{ .Static = buffer_size });
1416
15 pub fn flush(self: *Self) !void {17 pub fn flush(self: *Self) !void {
16 while (true) {18 try self.unbuffered_writer.writeAll(self.buf[0..self.end]);
17 const slice = self.fifo.readableSlice(0);19 self.end = 0;
18 if (slice.len == 0) break;
19 try self.unbuffered_writer.writeAll(slice);
20 self.fifo.discard(slice.len);
21 }
22 }20 }
2321
24 pub fn writer(self: *Self) Writer {22 pub fn writer(self: *Self) Writer {
...@@ -26,11 +24,14 @@ pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) ty...@@ -26,11 +24,14 @@ pub fn BufferedWriter(comptime buffer_size: usize, comptime WriterType: type) ty
26 }24 }
2725
28 pub fn write(self: *Self, bytes: []const u8) Error!usize {26 pub fn write(self: *Self, bytes: []const u8) Error!usize {
29 if (bytes.len >= self.fifo.writableLength()) {27 if (self.end + bytes.len > self.buf.len) {
30 try self.flush();28 try self.flush();
31 return self.unbuffered_writer.write(bytes);29 if (bytes.len > self.buf.len)
30 return self.unbuffered_writer.write(bytes);
32 }31 }
33 self.fifo.writeAssumeCapacity(bytes);32
33 mem.copy(u8, self.buf[self.end..], bytes);
34 self.end += bytes.len;
34 return bytes.len;35 return bytes.len;
35 }36 }
36 };37 };