writeLeb128

pub fn writeLeb128(w: *Writer, value: anytype) Error!void

File

Code

pub fn writeLeb128(w: *Writer, value: anytype) Error!void {
    const T = @TypeOf(value);
    const info = switch (@typeInfo(T)) {
        .int => |info| info,
        else => @compileError(@typeName(T) ++ " not supported"),
    };

    const BoundInt = @Int(info.signedness, 7);
    if (info.bits <= 7 or (value >= std.math.minInt(BoundInt) and value <= std.math.maxInt(BoundInt))) {
        const Bits = @Int(info.signedness, 8);
        const byte = switch (info.signedness) {
            .signed => @as(Bits, @intCast(value)) & 0x7F,
            .unsigned => @as(Bits, @intCast(value)),
        };
        try w.writeByte(@bitCast(byte));
        return;
    }

    const Byte = packed struct { bits: u7, more: bool };
    const Int = std.math.ByteAlignedInt(T);

    const max_bytes = @divFloor(info.bits - 1, 7) + 1;

    const sign_value = value >> (info.bits - 1);
    var val: Int = value;
    for (0..max_bytes) |_| {
        const more = switch (info.signedness) {
            .signed => val >> 6 != sign_value,
            .unsigned => val > std.math.maxInt(u7),
        };

        try w.writeByte(@bitCast(@as(Byte, .{
            .bits = @intCast(val & 0x7F),
            .more = more,
        })));

        if (!more) return;

        val >>= 7;
    } else unreachable;
}