Squeeze bits

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1

I was hoping letters would align on 64 bits so my struct would be 16 bytes.
How can I squeeze?
Somehow `‘letters’ bitsize = 128.

pub const Move = struct
{
    // 61 bits data
    pub const Data = packed struct
    {
         // 61 bits stuff
    };

    data: Data = .{},
    letters: std.BoundedArray(u8, 7) = .{},
}
2

BoundedArray stores a usize for the len.
You could implement it’s functionality yourself using a smaller len type

letters: [7]u8,
letterLen: u3,
3

OUCH of course! That usize.
Yes I rolled my own little Mini BoundedArray in there.

They should have comptimed that len variable :slight_smile:

4

They did and then walked back on it. I didn’t get why.

1 Like
5

Inb4 BoundedArrayUnmanaged where you need to pass the size yourself. :wink:

I guess storing size and not including it in the array type makes it more convenient to pass around.

6

So this minimal example does fit in 64 bits for TinyBoundedArray(u8, 7)

const std = @import("std");

pub fn TinyBoundedArray(comptime T: type, comptime capacity: u8) type
{
    return struct
    {
        const Self = @This();

        buffer: [capacity]T,
        len: u8 = 0,

        pub fn slice(self: *const Self)[]const T
        {
            return self.buffer[0..self.len];
        }

        fn append(self: *Self, value: T) void
        {
            self.buffer[self.len] = value;
            self.len += 1;
        }

        fn insert(self: *Self, value: T) void
        {
            if (self.len > 0) std.mem.copyBackwards(T, self.buffer[1..1 + self.len], self.buffer[0..self.len]);
            self.buffer[0] = value;
            self.len += 1;
        }
    };
}
1 Like
7

Actually, now I need a dynamic version just because of that usize.
That is less convenient. I need it for (test) building a trie where the nodes must not be to big.