zig/lib/std/fifo.zig

442 lines
16 KiB
Zig

// FIFO of fixed size items
// Usually used for e.g. byte buffers
const std = @import("std");
const math = std.math;
const mem = std.mem;
const Allocator = mem.Allocator;
const debug = std.debug;
const assert = debug.assert;
const testing = std.testing;
pub const LinearFifoBufferType = union(enum) {
/// The buffer is internal to the fifo; it is of the specified size.
Static: usize,
/// The buffer is passed as a slice to the initialiser.
Slice,
/// The buffer is managed dynamically using a `mem.Allocator`.
Dynamic,
};
pub fn LinearFifo(
comptime T: type,
comptime buffer_type: LinearFifoBufferType,
) type {
const autoalign = false;
const powers_of_two = switch (buffer_type) {
.Static => std.math.isPowerOfTwo(buffer_type.Static),
.Slice => false, // Any size slice could be passed in
.Dynamic => true, // This could be configurable in future
};
return struct {
allocator: if (buffer_type == .Dynamic) *Allocator else void,
buf: if (buffer_type == .Static) [buffer_type.Static]T else []T,
head: usize,
count: usize,
const Self = @This();
// Type of Self argument for slice operations.
// If buffer is inline (Static) then we need to ensure we haven't
// returned a slice into a copy on the stack
const SliceSelfArg = if (buffer_type == .Static) *Self else Self;
pub usingnamespace switch (buffer_type) {
.Static => struct {
pub fn init() Self {
return .{
.allocator = {},
.buf = undefined,
.head = 0,
.count = 0,
};
}
},
.Slice => struct {
pub fn init(buf: []T) Self {
return .{
.allocator = {},
.buf = buf,
.head = 0,
.count = 0,
};
}
},
.Dynamic => struct {
pub fn init(allocator: *Allocator) Self {
return .{
.allocator = allocator,
.buf = &[_]T{},
.head = 0,
.count = 0,
};
}
},
};
pub fn deinit(self: Self) void {
if (buffer_type == .Dynamic) self.allocator.free(self.buf);
}
pub fn realign(self: *Self) void {
if (self.buf.len - self.head >= self.count) {
// this copy overlaps
mem.copy(T, self.buf[0..self.count], self.buf[self.head..][0..self.count]);
self.head = 0;
} else {
var tmp: [mem.page_size / 2 / @sizeOf(T)]T = undefined;
while (self.head != 0) {
const n = math.min(self.head, tmp.len);
const m = self.buf.len - n;
mem.copy(T, tmp[0..n], self.buf[0..n]);
// this middle copy overlaps; the others here don't
mem.copy(T, self.buf[0..m], self.buf[n..][0..m]);
mem.copy(T, self.buf[m..], tmp[0..n]);
self.head -= n;
}
}
{ // set unused area to undefined
const unused = @sliceToBytes(self.buf[self.count..]);
@memset(unused.ptr, undefined, unused.len);
}
}
/// Reduce allocated capacity to `size`.
pub fn shrink(self: *Self, size: usize) void {
assert(size >= self.count);
if (buffer_type == .Dynamic) {
self.realign();
self.buf = self.allocator.realloc(self.buf, size) catch |e| switch (e) {
error.OutOfMemory => return, // no problem, capacity is still correct then.
};
}
}
/// Ensure that the buffer can fit at least `size` items
pub fn ensureCapacity(self: *Self, size: usize) !void {
if (self.buf.len >= size) return;
if (buffer_type == .Dynamic) {
self.realign();
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);
} else {
return error.OutOfMemory;
}
}
/// Makes sure at least `size` items are unused
pub fn ensureUnusedCapacity(self: *Self, size: usize) error{OutOfMemory}!void {
if (self.writableLength() >= size) return;
return try self.ensureCapacity(math.add(usize, self.count, size) catch return error.OutOfMemory);
}
/// Returns number of items currently in fifo
pub fn readableLength(self: Self) usize {
return self.count;
}
/// Returns a writable slice from the 'read' end of the fifo
fn readableSliceMut(self: SliceSelfArg, offset: usize) []T {
if (offset > self.count) return &[_]T{};
var start = self.head + offset;
if (start >= self.buf.len) {
start -= self.buf.len;
return self.buf[start .. self.count - offset];
} else {
const end = math.min(self.head + self.count, self.buf.len);
return self.buf[start..end];
}
}
/// Returns a readable slice from `offset`
pub fn readableSlice(self: SliceSelfArg, offset: usize) []const T {
return self.readableSliceMut(offset);
}
/// Discard first `count` bytes of readable data
pub fn discard(self: *Self, count: usize) void {
assert(count <= self.count);
{ // set old range to undefined. Note: may be wrapped around
const slice = self.readableSliceMut(0);
if (slice.len >= count) {
const unused = @sliceToBytes(slice[0..count]);
@memset(unused.ptr, undefined, unused.len);
} else {
const unused = @sliceToBytes(slice[0..]);
@memset(unused.ptr, undefined, unused.len);
const unused2 = @sliceToBytes(self.readableSliceMut(slice.len)[0 .. count - slice.len]);
@memset(unused2.ptr, undefined, unused2.len);
}
}
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
pub fn readItem(self: *Self) !T {
if (self.count == 0) return error.EndOfStream;
const c = self.buf[self.head];
self.discard(1);
return c;
}
/// Read data from the fifo into `dst`, returns number of bytes copied.
pub fn read(self: *Self, dst: []T) usize {
var dst_left = dst;
while (dst_left.len > 0) {
const slice = self.readableSlice(0);
if (slice.len == 0) break;
const n = math.min(slice.len, dst_left.len);
mem.copy(T, dst_left, slice[0..n]);
self.discard(n);
dst_left = dst_left[n..];
}
return dst.len - dst_left.len;
}
/// Returns number of bytes available in fifo
pub fn writableLength(self: Self) usize {
return self.buf.len - self.count;
}
/// Returns the first section of writable buffer
/// Note that this may be of length 0
pub fn writableSlice(self: SliceSelfArg, offset: usize) []T {
if (offset > self.buf.len) return &[_]T{};
const tail = self.head + offset + self.count;
if (tail < self.buf.len) {
return self.buf[tail..];
} else {
return self.buf[tail - self.buf.len ..][0 .. self.writableLength() - offset];
}
}
/// Returns a writable buffer of at least `size` bytes, allocating memory as needed.
/// Use `fifo.update` once you've written data to it.
pub fn writeableWithSize(self: *Self, size: usize) ![]T {
try self.ensureUnusedCapacity(size);
// try to avoid realigning buffer
var slice = self.writableSlice(0);
if (slice.len < size) {
self.realign();
slice = self.writableSlice(0);
}
return slice;
}
/// Update the tail location of the buffer (usually follows use of writable/writeableWithSize)
pub fn update(self: *Self, count: usize) void {
assert(self.count + count <= self.buf.len);
self.count += count;
}
/// Appends the data in `src` to the fifo.
/// You must have ensured there is enough space.
pub fn writeAssumeCapacity(self: *Self, src: []const T) void {
assert(self.writableLength() >= src.len);
var src_left = src;
while (src_left.len > 0) {
const writable_slice = self.writableSlice(0);
assert(writable_slice.len != 0);
const n = math.min(writable_slice.len, src_left.len);
mem.copy(T, writable_slice, src_left[0..n]);
self.update(n);
src_left = src_left[n..];
}
}
/// Write a single item to the fifo
pub fn writeItem(self: *Self, item: T) !void {
try self.ensureUnusedCapacity(1);
var tail = self.head + self.count;
if (powers_of_two) {
tail &= self.buf.len - 1;
} else {
tail %= self.buf.len;
}
self.buf[tail] = byte;
self.update(1);
}
/// Appends the data in `src` to the fifo.
/// Allocates more memory as necessary
pub fn write(self: *Self, src: []const T) !void {
try self.ensureUnusedCapacity(src.len);
return self.writeAssumeCapacity(src);
}
pub usingnamespace if (T == u8)
struct {
pub fn print(self: *Self, comptime format: []const u8, args: var) !void {
return std.fmt.format(self, error{OutOfMemory}, Self.write, format, args);
}
}
else
struct {};
/// Make `count` items available before the current read location
fn rewind(self: *Self, count: usize) void {
assert(self.writableLength() >= count);
var head = self.head + (self.buf.len - count);
if (powers_of_two) {
head &= self.buf.len - 1;
} else {
head %= self.buf.len;
}
self.head = head;
self.count += count;
}
/// Place data back into the read stream
pub fn unget(self: *Self, src: []const T) !void {
try self.ensureUnusedCapacity(src.len);
self.rewind(src.len);
const slice = self.readableSliceMut(0);
if (src.len < slice.len) {
mem.copy(T, slice, src);
} else {
mem.copy(T, slice, src[0..slice.len]);
const slice2 = self.readableSliceMut(slice.len);
mem.copy(T, slice2, src[slice.len..]);
}
}
/// Peek at the item at `offset`
pub fn peekItem(self: Self, offset: usize) error{EndOfStream}!T {
if (offset >= self.count)
return error.EndOfStream;
var index = self.head + offset;
if (powers_of_two) {
index &= self.buf.len - 1;
} else {
index %= self.buf.len;
}
return self.buf[index];
}
};
}
test "LinearFifo(u8, .Dynamic)" {
var fifo = LinearFifo(u8, .Dynamic).init(testing.allocator);
defer fifo.deinit();
try fifo.write("HELLO");
testing.expectEqual(@as(usize, 5), fifo.readableLength());
testing.expectEqualSlices(u8, "HELLO", fifo.readableSlice(0));
{
var i: usize = 0;
while (i < 5) : (i += 1) {
try fifo.write(&[_]u8{try fifo.peekItem(i)});
}
testing.expectEqual(@as(usize, 10), fifo.readableLength());
testing.expectEqualSlices(u8, "HELLOHELLO", fifo.readableSlice(0));
}
{
testing.expectEqual(@as(u8, 'H'), try fifo.readItem());
testing.expectEqual(@as(u8, 'E'), try fifo.readItem());
testing.expectEqual(@as(u8, 'L'), try fifo.readItem());
testing.expectEqual(@as(u8, 'L'), try fifo.readItem());
testing.expectEqual(@as(u8, 'O'), try fifo.readItem());
}
testing.expectEqual(@as(usize, 5), fifo.readableLength());
{ // Writes that wrap around
testing.expectEqual(@as(usize, 11), fifo.writableLength());
testing.expectEqual(@as(usize, 6), fifo.writableSlice(0).len);
fifo.writeAssumeCapacity("6<chars<11");
testing.expectEqualSlices(u8, "HELLO6<char", fifo.readableSlice(0));
testing.expectEqualSlices(u8, "s<11", fifo.readableSlice(11));
fifo.discard(11);
testing.expectEqualSlices(u8, "s<11", fifo.readableSlice(0));
fifo.discard(4);
testing.expectEqual(@as(usize, 0), fifo.readableLength());
}
{
const buf = try fifo.writeableWithSize(12);
testing.expectEqual(@as(usize, 12), buf.len);
var i: u8 = 0;
while (i < 10) : (i += 1) {
buf[i] = i + 'a';
}
fifo.update(10);
testing.expectEqualSlices(u8, "abcdefghij", fifo.readableSlice(0));
}
{
try fifo.unget("prependedstring");
var result: [30]u8 = undefined;
testing.expectEqualSlices(u8, "prependedstringabcdefghij", result[0..fifo.read(&result)]);
try fifo.unget("b");
try fifo.unget("a");
testing.expectEqualSlices(u8, "ab", result[0..fifo.read(&result)]);
}
fifo.shrink(0);
{
try fifo.print("{}, {}!", .{ "Hello", "World" });
var result: [30]u8 = undefined;
testing.expectEqualSlices(u8, "Hello, World!", result[0..fifo.read(&result)]);
testing.expectEqual(@as(usize, 0), fifo.readableLength());
}
}
test "LinearFifo" {
inline for ([_]type{ u1, u8, u16, u64 }) |T| {
inline for ([_]LinearFifoBufferType{ LinearFifoBufferType{ .Static = 32 }, .Slice, .Dynamic }) |bt| {
const FifoType = LinearFifo(T, bt);
var buf: if (bt == .Slice) [32]T else void = undefined;
var fifo = switch (bt) {
.Static => FifoType.init(),
.Slice => FifoType.init(buf[0..]),
.Dynamic => FifoType.init(testing.allocator),
};
defer fifo.deinit();
try fifo.write(&[_]T{ 0, 1, 1, 0, 1 });
testing.expectEqual(@as(usize, 5), fifo.readableLength());
{
testing.expectEqual(@as(T, 0), try fifo.readItem());
testing.expectEqual(@as(T, 1), try fifo.readItem());
testing.expectEqual(@as(T, 1), try fifo.readItem());
testing.expectEqual(@as(T, 0), try fifo.readItem());
testing.expectEqual(@as(T, 1), try fifo.readItem());
}
}
}
}