Undefined behavior on 16 bit architectures

[d2weber]

When I checked out this crate and used it as a path dependency, cargo warns be about several places with undefined behavior.

To reproduce:

git clone git@github.com:smoltcp-rs/smoltcp.git --branch v0.10.0

In a crate that uses a target with "target-pointer-width": "16" specify in Cargo.toml (assuming the directories are next to each other):

[dependency.smoltcp]
path= "../smoltcp"

When building/checking in the crate with the 16 bit target, cargo yields:

error: this arithmetic operation will overflow
   --> /home/dweber/gh/smoltcp/src/socket/tcp.rs:489:26
    |
489 |         if rx_capacity > (1 << 30) {
    |                          ^^^^^^^^^ attempt to shift left by `30_i32`, which would overflow
    |
    = note: `#[deny(arithmetic_overflow)]` on by default

error: this arithmetic operation will overflow
   --> /home/dweber/gh/smoltcp/src/socket/tcp.rs:597:13
    |
597 |             (1 << 16) - 1,
    |             ^^^^^^^^^ attempt to shift left by `16_i32`, which would overflow

error: this arithmetic operation will overflow
    --> /home/dweber/gh/smoltcp/src/socket/tcp.rs:2158:63
     |
2158 |                 repr.window_len = self.rx_buffer.window().min((1 << 16) - 1) as u16;
     |                                                               ^^^^^^^^^ attempt to shift left by `16_i32`, which would overflow

Note: if I specify the dependency as usual (smoltcp= "0.10.0"), these warnings won't appear but the behavior is still undefined.

[thvdveld]

Fixed in #983 .