Function writePackedTwosComplement [src]

Write the value of x to a packed memory buffer. Asserts that buffer is large enough to contain a value of bit-size bit_count at offset bit_offset. This is equivalent to storing the value of an integer with bit_count bits as if it were a field in packed memory at the provided bit offset.

Prototype

pub fn writePackedTwosComplement(x: Const, buffer: []u8, bit_offset: usize, bit_count: usize, endian: Endian) void

Parameters

x: Constbuffer: []u8bit_offset: usizebit_count: usizeendian: Endian

Source

  pub fn writePackedTwosComplement(x: Const, buffer: []u8, bit_offset: usize, bit_count: usize, endian: Endian) void {
    assert(x.fitsInTwosComp(if (x.positive) .unsigned else .signed, bit_count));

    // Copy all complete limbs
    var carry: u1 = 1;
    var limb_index: usize = 0;
    var bit_index: usize = 0;
    while (limb_index < bit_count / @bitSizeOf(Limb)) : (limb_index += 1) {
        var limb: Limb = if (limb_index < x.limbs.len) x.limbs[limb_index] else 0;

        // 2's complement (bitwise not, then add carry bit)
        if (!x.positive) {
            const ov = @addWithOverflow(~limb, carry);
            limb = ov[0];
            carry = ov[1];
        }

        // Write one Limb of bits
        mem.writePackedInt(Limb, buffer, bit_index + bit_offset, limb, endian);
        bit_index += @bitSizeOf(Limb);
    }

    // Copy the remaining bits
    if (bit_count != bit_index) {
        var limb: Limb = if (limb_index < x.limbs.len) x.limbs[limb_index] else 0;

        // 2's complement (bitwise not, then add carry bit)
        if (!x.positive) limb = ~limb +% carry;

        // Write all remaining bits
        mem.writeVarPackedInt(buffer, bit_index + bit_offset, bit_count - bit_index, limb, endian);
    }
}  