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std: add optimization to fifo if size is power of two

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daurnimator 2019-11-11 00:26:40 +11:00
parent 01b2a56225
commit e810f485ab
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GPG Key ID: 45B429A8F9D9D22A
1 changed files with 30 additions and 7 deletions
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37
lib/std/fifo.zig
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@ -12,6 +12,8 @@ const testing = std.testing;
pub fn FixedSizeFifo(comptime T: type) type {
const autoalign = false;
const powers_of_two = true;
return struct {
allocator: *Allocator,
buf: []T,
@ -68,10 +70,10 @@ pub fn FixedSizeFifo(comptime T: type) type {
}
/// Ensure that the buffer can fit at least `size` items
pub fn ensureCapacity(self: *Self, size: usize) error{OutOfMemory}!void {
pub fn ensureCapacity(self: *Self, size: usize) !void {
if (self.buf.len >= size) return;
self.realign();
const new_size = math.ceilPowerOfTwo(usize, size) catch return error.OutOfMemory;
const new_size = if (powers_of_two) math.ceilPowerOfTwo(usize, size) catch return error.OutOfMemory else size;
self.buf = try self.allocator.realloc(self.buf, new_size);
}
@ -124,10 +126,19 @@ pub fn FixedSizeFifo(comptime T: type) type {
@memset(unused2.ptr, undefined, unused2.len);
}
}
self.head = (self.head + count) % self.buf.len;
self.count -= count;
if (autoalign and self.count == 0)
if (autoalign and self.count == count) {
self.head = 0;
self.count = 0;
} else {
var head = self.head + count;
if (powers_of_two) {
head &= self.buf.len - 1;
} else {
head %= self.buf.len;
}
self.head = head;
self.count -= count;
}
}
/// Read the next item from the fifo
@ -225,7 +236,13 @@ pub fn FixedSizeFifo(comptime T: type) type {
fn rewind(self: *Self, size: usize) void {
assert(self.writableLength() >= size);
self.head = (self.head + (self.buf.len - size)) % self.buf.len;
var head = self.head + (self.buf.len - size);
if (powers_of_two) {
head &= self.buf.len - 1;
} else {
head %= self.buf.len;
}
self.head = head;
self.count += size;
}
@ -246,7 +263,13 @@ pub fn FixedSizeFifo(comptime T: type) type {
if (offset >= self.count)
return error.EndOfStream;
return self.buf[(self.head + offset) % self.buf.len];
var index = self.head + offset;
if (powers_of_two) {
index &= self.buf.len - 1;
} else {
index %= self.buf.len;
}
return self.buf[index];
}
};
}