setTwosCompIntLimit

    pub fn setTwosCompIntLimit(
        r: *Mutable,
        limit: TwosCompIntLimit,
        signedness: Signedness,
        bit_count: usize,
    ) void {
        // Handle zero-bit types.
        if (bit_count == 0) {
            r.set(0);
            return;
        }

        const req_limbs = calcTwosCompLimbCount(bit_count);
        const bit: Log2Limb = @truncate(bit_count - 1);
        const signmask = @as(Limb, 1) << bit; // 0b0..010..0 where 1 is the sign bit.
        const mask = (signmask << 1) -% 1; // 0b0..011..1 where the leftmost 1 is the sign bit.

        r.positive = true;

        switch (signedness) {
            .signed => switch (limit) {
                .min => {
                    // Negative bound, signed = -0x80.
                    r.len = req_limbs;
                    @memset(r.limbs[0 .. r.len - 1], 0);
                    r.limbs[r.len - 1] = signmask;
                    r.positive = false;
                },
                .max => {
                    // Positive bound, signed = 0x7F
                    // Note, in this branch we need to normalize because the first bit is
                    // supposed to be 0.

                    // Special case for 1-bit integers.
                    if (bit_count == 1) {
                        r.set(0);
                    } else {
                        const new_req_limbs = calcTwosCompLimbCount(bit_count - 1);
                        const msb = @as(Log2Limb, @truncate(bit_count - 2));
                        const new_signmask = @as(Limb, 1) << msb; // 0b0..010..0 where 1 is the sign bit.
                        const new_mask = (new_signmask << 1) -% 1; // 0b0..001..1 where the rightmost 0 is the sign bit.

                        r.len = new_req_limbs;
                        @memset(r.limbs[0 .. r.len - 1], maxInt(Limb));
                        r.limbs[r.len - 1] = new_mask;
                    }
                },
            },
            .unsigned => switch (limit) {
                .min => {
                    // Min bound, unsigned = 0x00
                    r.set(0);
                },
                .max => {
                    // Max bound, unsigned = 0xFF
                    r.len = req_limbs;
                    @memset(r.limbs[0 .. r.len - 1], maxInt(Limb));
                    r.limbs[r.len - 1] = mask;
                },
            },
        }
    }