307 lines
11 KiB
Zig
307 lines
11 KiB
Zig
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const std = @import("std");
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const builtin = @import("builtin");
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const testing = std.testing;
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///
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/// A bitmap that uses a specific type to store the entries.
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///
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/// Arguments:
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/// IN BitmapType: type - The integer type to use to store entries.
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///
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/// Return: type.
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/// The bitmap type created.
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///
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pub fn Bitmap(comptime BitmapType: type) type {
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return struct {
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/// The possible errors thrown by bitmap functions
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pub const BitmapError = error{
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/// The address given was outside the region covered by a bitmap
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OutOfBounds,
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};
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const Self = @This();
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/// The number of entries that one bitmap type can hold. Evaluates to the number of bits the type has
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pub const ENTRIES_PER_BITMAP: u32 = std.meta.bitCount(BitmapType);
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/// The value that a full bitmap will have
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pub const BITMAP_FULL = std.math.maxInt(BitmapType);
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/// The type of an index into a bitmap entry. The smallest integer needed to represent all bit positions in the bitmap entry type
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pub const IndexType = @Type(builtin.TypeInfo{ .Int = builtin.TypeInfo.Int{ .is_signed = false, .bits = std.math.log2(std.meta.bitCount(BitmapType)) } });
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num_bitmaps: u32,
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num_entries: u32,
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bitmaps: []BitmapType,
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num_free_entries: u32,
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///
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/// Create an instance of this bitmap type.
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///
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/// Arguments:
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/// IN num_entries: u32 - The number of entries that the bitmap created will have.
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/// The number of BitmapType required to store this many entries will be allocated and each will be zeroed.
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/// IN allocator: *std.mem.Allocator - The allocator to use when allocating the BitmapTypes required.
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///
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/// Return: Self.
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/// The bitmap instance.
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///
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/// Error: std.mem.Allocator.Error
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/// OutOfMemory: There isn't enough memory available to allocate the required number of BitmapType.
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///
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pub fn init(num_entries: u32, allocator: *std.mem.Allocator) !Self {
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const num = @floatToInt(u32, @ceil(@intToFloat(f32, num_entries) / @intToFloat(f32, ENTRIES_PER_BITMAP)));
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const self = Self{
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.num_bitmaps = num,
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.num_entries = num_entries,
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.bitmaps = try allocator.alloc(BitmapType, num),
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.num_free_entries = num_entries,
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};
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for (self.bitmaps) |*bmp| {
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bmp.* = 0;
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}
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return self;
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}
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///
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/// Set an entry within a bitmap as occupied.
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///
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/// Arguments:
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/// INOUT self: *Self - The bitmap to modify.
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/// IN idx: BitmapIndex - The index within the bitmap to set.
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///
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/// Error: BitmapError.
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/// OutOfBounds: The index given is out of bounds.
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///
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pub fn setEntry(self: *Self, idx: u32) BitmapError!void {
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if (idx >= self.num_entries) return BitmapError.OutOfBounds;
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if (!try self.isSet(idx)) {
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const bit = self.indexToBit(idx);
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self.bitmaps[idx / ENTRIES_PER_BITMAP] |= bit;
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self.num_free_entries -= 1;
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}
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}
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///
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/// Set an entry within a bitmap as unoccupied.
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///
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/// Arguments:
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/// INOUT self: *Self - The bitmap to modify.
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/// IN idx: BitmapIndex - The index within the bitmap to clear.
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///
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/// Error: BitmapError.
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/// OutOfBounds: The index given is out of bounds.
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///
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pub fn clearEntry(self: *Self, idx: u32) BitmapError!void {
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if (idx >= self.num_entries) return BitmapError.OutOfBounds;
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if (try self.isSet(idx)) {
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const bit = self.indexToBit(idx);
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self.bitmaps[idx / ENTRIES_PER_BITMAP] &= ~bit;
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self.num_free_entries += 1;
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}
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}
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///
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/// Convert a global bitmap index into the bit corresponding to an entry within a single BitmapType.
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///
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/// Arguments:
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/// IN self: *Self - The bitmap to use.
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/// IN idx: u32 - The index into all of the bitmap's entries.
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///
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/// Return: BitmapType.
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/// The bit corresponding to that index but within a single BitmapType.
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///
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fn indexToBit(self: *Self, idx: u32) BitmapType {
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return @as(BitmapType, 1) << @intCast(IndexType, idx % ENTRIES_PER_BITMAP);
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}
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///
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/// Set the first free entry within the bitmaps as occupied.
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///
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/// Return: ?u32.
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/// The index within all bitmaps that was set or null if there wasn't one free.
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/// 0 .. ENTRIES_PER_BITMAP - 1 if in the first bitmap, ENTRIES_PER_BITMAP .. ENTRIES_PER_BITMAP * 2 - 1 if in the second etc.
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///
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pub fn setFirstFree(self: *Self) ?u32 {
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if (self.num_free_entries == 0) return null;
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for (self.bitmaps) |*bmp, i| {
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if (bmp.* == BITMAP_FULL)
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continue;
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const bit = @truncate(IndexType, @ctz(BitmapType, ~bmp.*));
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const idx = bit + @intCast(u32, i) * ENTRIES_PER_BITMAP;
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// Failing here means that the index is outside of the bitmap, so there are no free entries
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self.setEntry(idx) catch return null;
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return idx;
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}
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return null;
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}
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///
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/// Check if an entry is set.
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///
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/// Arguments:
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/// IN self: *Bitmap - The bitmap to check.
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/// IN idx: u32 - The entry to check.
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///
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/// Return: bool.
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/// True if the entry is set, else false.
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///
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/// Error: BitmapError.
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/// OutOfBounds: The index given is out of bounds.
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///
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pub fn isSet(self: *Self, idx: u32) BitmapError!bool {
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if (idx >= self.num_entries) return BitmapError.OutOfBounds;
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return (self.bitmaps[idx / ENTRIES_PER_BITMAP] & self.indexToBit(idx)) != 0;
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}
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};
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}
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test "setEntry" {
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var bmp = try Bitmap(u32).init(31, std.heap.direct_allocator);
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testing.expectEqual(@as(u32, 31), bmp.num_free_entries);
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try bmp.setEntry(0);
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testing.expectEqual(@as(u32, 1), bmp.bitmaps[0]);
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testing.expectEqual(@as(u32, 30), bmp.num_free_entries);
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try bmp.setEntry(1);
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testing.expectEqual(@as(u32, 3), bmp.bitmaps[0]);
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testing.expectEqual(@as(u32, 29), bmp.num_free_entries);
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// Repeat setting entry 1 to make sure state doesn't change
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try bmp.setEntry(1);
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testing.expectEqual(@as(u32, 3), bmp.bitmaps[0]);
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testing.expectEqual(@as(u32, 29), bmp.num_free_entries);
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testing.expectError(Bitmap(u32).BitmapError.OutOfBounds, bmp.setEntry(31));
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testing.expectEqual(@as(u32, 29), bmp.num_free_entries);
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}
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test "clearEntry" {
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var bmp = try Bitmap(u32).init(32, std.heap.direct_allocator);
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testing.expectEqual(@as(u32, 32), bmp.num_free_entries);
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try bmp.setEntry(0);
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testing.expectEqual(@as(u32, 31), bmp.num_free_entries);
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try bmp.setEntry(1);
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testing.expectEqual(@as(u32, 30), bmp.num_free_entries);
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testing.expectEqual(@as(u32, 3), bmp.bitmaps[0]);
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try bmp.clearEntry(0);
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testing.expectEqual(@as(u32, 31), bmp.num_free_entries);
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testing.expectEqual(@as(u32, 2), bmp.bitmaps[0]);
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// Repeat to make sure state doesn't change
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try bmp.clearEntry(0);
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testing.expectEqual(@as(u32, 31), bmp.num_free_entries);
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testing.expectEqual(@as(u32, 2), bmp.bitmaps[0]);
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// Try clearing an unset entry to make sure state doesn't change
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try bmp.clearEntry(2);
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testing.expectEqual(@as(u32, 31), bmp.num_free_entries);
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testing.expectEqual(@as(u32, 2), bmp.bitmaps[0]);
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testing.expectError(Bitmap(u32).BitmapError.OutOfBounds, bmp.clearEntry(32));
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}
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test "setFirstFree multiple bitmaps" {
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var bmp = try Bitmap(u8).init(9, std.heap.direct_allocator);
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// Allocate the first entry
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, 0);
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testing.expectEqual(bmp.bitmaps[0], 1);
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// Allocate the second entry
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, 1);
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testing.expectEqual(bmp.bitmaps[0], 3);
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// Allocate the entirety of the first bitmap
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var entry: u32 = 2;
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var expected: u8 = 7;
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while (entry < Bitmap(u8).ENTRIES_PER_BITMAP) {
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, entry);
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testing.expectEqual(bmp.bitmaps[0], expected);
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if (entry + 1 < Bitmap(u8).ENTRIES_PER_BITMAP) {
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entry += 1;
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expected = expected * 2 + 1;
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} else {
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break;
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}
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}
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// Try allocating an entry in the next bitmap
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, Bitmap(u8).ENTRIES_PER_BITMAP);
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testing.expectEqual(bmp.bitmaps[0], Bitmap(u8).BITMAP_FULL);
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testing.expectEqual(bmp.bitmaps[1], 1);
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// We should no longer be able to allocate any entries
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testing.expectEqual(bmp.setFirstFree(), null);
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testing.expectEqual(bmp.bitmaps[0], Bitmap(u8).BITMAP_FULL);
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testing.expectEqual(bmp.bitmaps[1], 1);
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}
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test "setFirstFree" {
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var bmp = try Bitmap(u32).init(32, std.heap.direct_allocator);
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// Allocate the first entry
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, 0);
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testing.expectEqual(bmp.bitmaps[0], 1);
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// Allocate the second entry
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, 1);
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testing.expectEqual(bmp.bitmaps[0], 3);
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// Make all but the MSB occupied and try to allocate it
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bmp.bitmaps[0] = Bitmap(u32).BITMAP_FULL & ~@as(u32, 1 << (Bitmap(u32).ENTRIES_PER_BITMAP - 1));
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testing.expectEqual(bmp.setFirstFree() orelse unreachable, Bitmap(u32).ENTRIES_PER_BITMAP - 1);
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testing.expectEqual(bmp.bitmaps[0], Bitmap(u32).BITMAP_FULL);
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// We should no longer be able to allocate any entries
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testing.expectEqual(bmp.setFirstFree(), null);
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testing.expectEqual(bmp.bitmaps[0], Bitmap(u32).BITMAP_FULL);
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}
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test "isSet" {
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var bmp = try Bitmap(u32).init(32, std.heap.direct_allocator);
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bmp.bitmaps[0] = 1;
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// Make sure that only the set entry is considered set
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testing.expect(try bmp.isSet(0));
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var i: u32 = 1;
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while (i < bmp.num_entries) : (i += 1) {
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testing.expect(!try bmp.isSet(i));
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}
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bmp.bitmaps[0] = 3;
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testing.expect(try bmp.isSet(0));
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testing.expect(try bmp.isSet(1));
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i = 2;
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while (i < bmp.num_entries) : (i += 1) {
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testing.expect(!try bmp.isSet(i));
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}
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bmp.bitmaps[0] = 11;
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testing.expect(try bmp.isSet(0));
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testing.expect(try bmp.isSet(1));
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testing.expect(!try bmp.isSet(2));
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testing.expect(try bmp.isSet(3));
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i = 4;
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while (i < bmp.num_entries) : (i += 1) {
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testing.expect(!try bmp.isSet(i));
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}
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testing.expectError(Bitmap(u32).BitmapError.OutOfBounds, bmp.isSet(33));
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}
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test "indexToBit" {
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var bmp = try Bitmap(u8).init(10, std.heap.direct_allocator);
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testing.expectEqual(bmp.indexToBit(0), 1);
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testing.expectEqual(bmp.indexToBit(1), 2);
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testing.expectEqual(bmp.indexToBit(2), 4);
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testing.expectEqual(bmp.indexToBit(3), 8);
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testing.expectEqual(bmp.indexToBit(4), 16);
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testing.expectEqual(bmp.indexToBit(5), 32);
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testing.expectEqual(bmp.indexToBit(6), 64);
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testing.expectEqual(bmp.indexToBit(7), 128);
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testing.expectEqual(bmp.indexToBit(8), 1);
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testing.expectEqual(bmp.indexToBit(9), 2);
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}
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