319 lines
11 KiB
Zig
319 lines
11 KiB
Zig
// FIFO of fixed size items
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// Usually used for e.g. byte buffers
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const std = @import("std");
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const math = std.math;
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const mem = std.mem;
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const Allocator = mem.Allocator;
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const debug = std.debug;
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const assert = debug.assert;
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const testing = std.testing;
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pub fn FixedSizeFifo(comptime T: type) type {
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return struct {
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allocator: *Allocator,
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buf: []u8,
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head: usize,
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count: usize,
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const Self = @This();
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pub fn init(allocator: *Allocator) Self {
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return Self{
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.allocator = allocator,
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.buf = [_]T{},
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.head = 0,
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.count = 0,
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};
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}
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pub fn deinit(self: *Self) void {
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self.allocator.free(self.buf);
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self.* = undefined;
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}
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pub fn realign(self: *Self) void {
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if (self.buf.len - self.head >= self.count) {
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// this copy overlaps
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mem.copy(T, self.buf[0..self.count], self.buf[self.head..][0..self.count]);
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self.head = 0;
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} else {
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var tmp: [mem.page_size / 2 / @sizeOf(T)]T = undefined;
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while (self.head != 0) {
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const n = math.min(self.head, tmp.len);
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const m = self.buf.len - n;
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mem.copy(T, tmp[0..n], self.buf[0..n]);
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// this middle copy overlaps; the others here don't
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mem.copy(T, self.buf[0..m], self.buf[n..][0..m]);
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mem.copy(T, self.buf[m..], tmp[0..n]);
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self.head -= n;
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}
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}
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{ // set unused area to undefined
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const unused = @sliceToBytes(self.buf[self.count..]);
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@memset(unused.ptr, undefined, unused.len);
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}
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}
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/// Reduce allocated capacity to `size`.
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pub fn shrink(self: *Self, size: usize) void {
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assert(size >= self.count);
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self.realign();
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self.buf = self.allocator.realloc(self.buf, size) catch |e| switch (e) {
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error.OutOfMemory => return, // no problem, capacity is still correct then.
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};
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}
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/// Ensure that the buffer can fit at least `size` items
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pub fn ensureCapacity(self: *Self, size: usize) error{OutOfMemory}!void {
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if (self.buf.len >= size) return;
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self.realign();
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const new_size = math.ceilPowerOfTwo(usize, size) catch return error.OutOfMemory;
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self.buf = try self.allocator.realloc(self.buf, new_size);
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}
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/// Makes sure at least `size` items are unused
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pub fn ensureUnusedCapacity(self: *Self, size: usize) error{OutOfMemory}!void {
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if (self.writableLength() >= size) return;
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return try self.ensureCapacity(math.add(usize, self.count, size) catch return error.OutOfMemory);
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}
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/// Returns number of items currently in fifo
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pub fn readableLength(self: Self) usize {
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return self.count;
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}
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/// Returns a writable slice from the 'read' end of the fifo
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fn readableSliceMut(self: Self, offset: usize) []T {
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if (offset > self.count) return [_]T{};
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const start = self.head + offset;
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if (start >= self.buf.len) {
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return self.buf[start - self.buf.len ..][0 .. self.count - offset];
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} else {
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const end: usize = self.head + self.count;
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if (end >= self.buf.len) {
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return self.buf[start..self.buf.len];
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} else {
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return self.buf[start..end];
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}
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}
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}
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/// Returns a readable slice from `offset`
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pub fn readableSlice(self: Self, offset: usize) []const T {
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return self.readableSliceMut(offset);
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}
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const autoalign = false;
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/// Discard first `count` bytes of readable data
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pub fn discard(self: *Self, count: usize) void {
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assert(count <= self.count);
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{ // set old range to undefined. Note: may be wrapped around
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const slice = self.readableSliceMut(0);
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if (slice.len >= count) {
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const unused = @sliceToBytes(slice[0..count]);
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@memset(unused.ptr, undefined, unused.len);
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} else {
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const unused = @sliceToBytes(slice[0..]);
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@memset(unused.ptr, undefined, unused.len);
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const unused2 = @sliceToBytes(self.readableSliceMut(slice.len)[0 .. count - slice.len]);
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@memset(unused2.ptr, undefined, unused2.len);
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}
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}
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self.head = (self.head + count) % self.buf.len;
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self.count -= count;
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if (autoalign and self.count == 0)
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self.head = 0;
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}
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/// Read the next item from the fifo
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pub fn readItem(self: *Self) !T {
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if (self.count == 0) return error.EndOfStream;
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const c = self.buf[self.head];
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self.discard(1);
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return c;
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}
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/// Read data from the fifo into `dst`, returns slice of bytes copied (subslice of `dst`)
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pub fn read(self: *Self, dst: []T) []T {
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var dst_left = dst;
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while (dst_left.len > 0) {
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const slice = self.readableSlice(0);
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if (slice.len == 0) break;
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const n = math.min(slice.len, dst_left.len);
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mem.copy(T, dst_left, slice[0..n]);
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self.discard(n);
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dst_left = dst_left[n..];
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}
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return dst[0 .. dst.len - dst_left.len];
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}
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/// Returns number of bytes available in fifo
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pub fn writableLength(self: Self) usize {
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return self.buf.len - self.count;
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}
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/// Returns the first section of writable buffer
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/// Note that this may be of length 0
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pub fn writableSlice(self: Self, offset: usize) []T {
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if (offset > self.buf.len) return [_]T{};
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const tail = self.head + offset + self.count;
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if (tail < self.buf.len) {
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return self.buf[tail..];
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} else {
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return self.buf[tail - self.buf.len ..][0 .. self.writableLength() - offset];
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}
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}
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/// Returns a writable buffer of at least `size` bytes, allocating memory as needed.
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/// Use `fifo.update` once you've written data to it.
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pub fn writeableWithSize(self: *Self, size: usize) ![]T {
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try self.ensureUnusedCapacity(size);
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// try to avoid realigning buffer
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var slice = self.writableSlice(0);
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if (slice.len < size) {
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self.realign();
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slice = self.writableSlice(0);
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}
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return slice;
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}
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/// Update the tail location of the buffer (usually follows use of writable/writeableWithSize)
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pub fn update(self: *Self, count: usize) void {
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assert(self.count + count <= self.buf.len);
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self.count += count;
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}
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/// Appends the data in `src` to the fifo. You must
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pub fn writeAssumeCapacity(self: *Self, src: []const T) void {
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assert(self.writableLength() >= src.len);
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var src_left = src;
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while (src_left.len > 0) {
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const writable_slice = self.writableSlice(0);
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assert(writable_slice.len != 0);
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const n = math.min(writable_slice.len, src_left.len);
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mem.copy(T, writable_slice, src_left[0..n]);
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self.update(n);
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src_left = src_left[n..];
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}
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}
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/// Appends the data in `src` to the fifo.
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/// Allocates more memory as necessary
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pub fn write(self: *Self, src: []const T) !void {
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try self.ensureUnusedCapacity(src.len);
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return self.writeAssumeCapacity(src);
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}
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pub fn print(self: *Self, comptime format: []const u8, args: ...) !void {
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return std.fmt.format(self, error{OutOfMemory}, Self.write, format, args);
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}
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/// Make `count` bytes available before the current read location
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fn rewind(self: *Self, size: usize) void {
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assert(self.writableLength() >= size);
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self.head = (self.head + (self.buf.len - size)) % self.buf.len;
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self.count += size;
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}
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/// Place data back into the read stream
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pub fn unget(self: *Self, src: []const T) !void {
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try self.ensureUnusedCapacity(src.len);
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self.rewind(src.len);
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const slice = self.readableSliceMut(0);
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mem.copy(T, slice, src[0..slice.len]);
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const slice2 = self.readableSliceMut(slice.len);
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mem.copy(T, slice2, src[slice.len..]);
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}
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/// Peek at the item at `offset`
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pub fn peekItem(self: Self, offset: usize) error{EndOfStream}!T {
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if (offset >= self.count)
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return error.EndOfStream;
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return self.buf[(self.head + offset) % self.buf.len];
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}
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};
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}
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const ByteFifo = FixedSizeFifo(u8);
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test "ByteFifo" {
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var fifo = ByteFifo.init(debug.global_allocator);
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defer fifo.deinit();
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try fifo.write("HELLO");
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testing.expectEqual(usize(5), fifo.readableLength());
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testing.expectEqualSlices(u8, "HELLO", fifo.readableSlice(0));
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{
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var i: usize = 0;
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while (i < 5) : (i += 1) {
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try fifo.write([_]u8{try fifo.peekItem(i)});
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}
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testing.expectEqual(usize(10), fifo.readableLength());
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testing.expectEqualSlices(u8, "HELLOHELLO", fifo.readableSlice(0));
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}
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{
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testing.expectEqual(u8('H'), try fifo.readItem());
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testing.expectEqual(u8('E'), try fifo.readItem());
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testing.expectEqual(u8('L'), try fifo.readItem());
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testing.expectEqual(u8('L'), try fifo.readItem());
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testing.expectEqual(u8('O'), try fifo.readItem());
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}
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testing.expectEqual(usize(5), fifo.readableLength());
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{ // Writes that wrap around
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testing.expectEqual(usize(11), fifo.writableLength());
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testing.expectEqual(usize(6), fifo.writableSlice(0).len);
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fifo.writeAssumeCapacity("6<chars<11");
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testing.expectEqualSlices(u8, "HELLO6<char", fifo.readableSlice(0));
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testing.expectEqualSlices(u8, "s<11", fifo.readableSlice(11));
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fifo.discard(11);
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testing.expectEqualSlices(u8, "s<11", fifo.readableSlice(0));
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fifo.discard(4);
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testing.expectEqual(usize(0), fifo.readableLength());
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}
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{
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const buf = try fifo.writeableWithSize(12);
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testing.expectEqual(usize(12), buf.len);
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var i: u8 = 0;
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while (i < 10) : (i += 1) {
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buf[i] = i + 'a';
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}
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fifo.update(10);
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testing.expectEqualSlices(u8, "abcdefghij", fifo.readableSlice(0));
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}
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{
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try fifo.unget("prependedstring");
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var result: [30]u8 = undefined;
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testing.expectEqualSlices(u8, "prependedstringabcdefghij", fifo.read(&result));
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}
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fifo.shrink(0);
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{
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try fifo.print("{}, {}!", "Hello", "World");
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var result: [30]u8 = undefined;
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testing.expectEqualSlices(u8, "Hello, World!", fifo.read(&result));
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testing.expectEqual(usize(0), fifo.readableLength());
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}
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}
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