1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2021 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
const std = @import("../std.zig");
const meta = std.meta;
const testing = std.testing;
const mem = std.mem;
const assert = std.debug.assert;
const TypeInfo = std.builtin.TypeInfo;
/// This is useful for saving memory when allocating an object that has many
/// optional components. The optional objects are allocated sequentially in
/// memory, and a single integer is used to represent each optional object
/// and whether it is present based on each corresponding bit.
pub fn TrailerFlags(comptime Fields: type) type {
return struct {
bits: Int,
pub const Int = meta.Int(.unsigned, bit_count);
pub const bit_count = @typeInfo(Fields).Struct.fields.len;
pub const FieldEnum = std.meta.FieldEnum(Fields);
pub const InitStruct = blk: {
comptime var fields: [bit_count]TypeInfo.StructField = undefined;
inline for (@typeInfo(Fields).Struct.fields) |struct_field, i| {
fields[i] = TypeInfo.StructField{
.name = struct_field.name,
.field_type = ?struct_field.field_type,
.default_value = @as(
??struct_field.field_type,
@as(?struct_field.field_type, null),
),
.is_comptime = false,
.alignment = @alignOf(?struct_field.field_type),
};
}
break :blk @Type(.{
.Struct = .{
.layout = .Auto,
.fields = &fields,
.decls = &[_]TypeInfo.Declaration{},
.is_tuple = false,
},
});
};
pub const Self = @This();
pub fn has(self: Self, comptime field: FieldEnum) bool {
const field_index = @enumToInt(field);
return (self.bits & (1 << field_index)) != 0;
}
pub fn get(self: Self, p: [*]align(@alignOf(Fields)) const u8, comptime field: FieldEnum) ?Field(field) {
if (!self.has(field))
return null;
return self.ptrConst(p, field).*;
}
pub fn setFlag(self: *Self, comptime field: FieldEnum) void {
const field_index = @enumToInt(field);
self.bits |= 1 << field_index;
}
/// `fields` is a struct with each field set to an optional value.
/// Only the non-null bits are observed and are used to set the flag bits.
pub fn init(fields: InitStruct) Self {
var self: Self = .{ .bits = 0 };
inline for (@typeInfo(Fields).Struct.fields) |field, i| {
if (@field(fields, field.name)) |_|
self.bits |= 1 << i;
}
return self;
}
/// `fields` is a struct with each field set to an optional value (same as `init`).
pub fn setMany(self: Self, p: [*]align(@alignOf(Fields)) u8, fields: InitStruct) void {
inline for (@typeInfo(Fields).Struct.fields) |field, i| {
if (@field(fields, field.name)) |value|
self.set(p, @intToEnum(FieldEnum, i), value);
}
}
pub fn set(
self: Self,
p: [*]align(@alignOf(Fields)) u8,
comptime field: FieldEnum,
value: Field(field),
) void {
self.ptr(p, field).* = value;
}
pub fn ptr(self: Self, p: [*]align(@alignOf(Fields)) u8, comptime field: FieldEnum) *Field(field) {
if (@sizeOf(Field(field)) == 0)
return undefined;
const off = self.offset(p, field);
return @ptrCast(*Field(field), @alignCast(@alignOf(Field(field)), p + off));
}
pub fn ptrConst(self: Self, p: [*]align(@alignOf(Fields)) const u8, comptime field: FieldEnum) *const Field(field) {
if (@sizeOf(Field(field)) == 0)
return undefined;
const off = self.offset(p, field);
return @ptrCast(*const Field(field), @alignCast(@alignOf(Field(field)), p + off));
}
pub fn offset(self: Self, p: [*]align(@alignOf(Fields)) const u8, comptime field: FieldEnum) usize {
var off: usize = 0;
inline for (@typeInfo(Fields).Struct.fields) |field_info, i| {
const active = (self.bits & (1 << i)) != 0;
if (i == @enumToInt(field)) {
assert(active);
return mem.alignForwardGeneric(usize, off, @alignOf(field_info.field_type));
} else if (active) {
off = mem.alignForwardGeneric(usize, off, @alignOf(field_info.field_type));
off += @sizeOf(field_info.field_type);
}
}
}
pub fn Field(comptime field: FieldEnum) type {
return @typeInfo(Fields).Struct.fields[@enumToInt(field)].field_type;
}
pub fn sizeInBytes(self: Self) usize {
var off: usize = 0;
inline for (@typeInfo(Fields).Struct.fields) |field, i| {
if (@sizeOf(field.field_type) == 0)
continue;
if ((self.bits & (1 << i)) != 0) {
off = mem.alignForwardGeneric(usize, off, @alignOf(field.field_type));
off += @sizeOf(field.field_type);
}
}
return off;
}
};
}
test "TrailerFlags" {
const Flags = TrailerFlags(struct {
a: i32,
b: bool,
c: u64,
});
testing.expectEqual(u2, @TagType(Flags.FieldEnum));
var flags = Flags.init(.{
.b = true,
.c = 1234,
});
const slice = try testing.allocator.allocAdvanced(u8, 8, flags.sizeInBytes(), .exact);
defer testing.allocator.free(slice);
flags.set(slice.ptr, .b, false);
flags.set(slice.ptr, .c, 12345678);
testing.expect(flags.get(slice.ptr, .a) == null);
testing.expect(!flags.get(slice.ptr, .b).?);
testing.expect(flags.get(slice.ptr, .c).? == 12345678);
flags.setMany(slice.ptr, .{
.b = true,
.c = 5678,
});
testing.expect(flags.get(slice.ptr, .a) == null);
testing.expect(flags.get(slice.ptr, .b).?);
testing.expect(flags.get(slice.ptr, .c).? == 5678);
}
|
