C#C
C#•4y ago•
10 replies
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Parsing a string into a Vector of bytes most efficiently

Given a string with an even amount of characters, what's the most efficient way to parse that into a Vector<byte> along with another Vector<byte> of bit masks?

A sample input is 12 34 ?? 78 87 ?5 ?3 21 -- these are meant to be hex bytes -- which would get turned into < 0x12 0x34 0x00 0x78 0x87 0x05 0x03 0x21 > for the values, and < 0xFF 0xFF 0x00 0xFF 0xFF 0x0F 0x0F 0xFF > for the masks.

Currently I'm doing the input.Length % 2 != 0 check first, of course, followed by Regex.Matches(input, @"..").Select(match => match.Value).ToList();.
From here I do this to parse all of the bytes;

int length = bytes.Length;
if (length < Vector<byte>.Count)
    length = Vector<byte>.Count;

byte[] values = new byte[length], masks = new byte[length];

for (int i = 0; i < bytes.Length; i++)
{
    var currByte = bytes[i];

    var hasUpper = byte.TryParse(currByte[0].ToString(), NumberStyles.HexNumber, null, out byte upper);
    var hasLower = byte.TryParse(currByte[1].ToString(), NumberStyles.HexNumber, null, out byte lower);

    switch ((hasUpper, hasLower))
    {
        case (true, true):
        {
            values[i] = (byte)((upper << 4) + lower);
            masks[i] = 0xFF;
            break;
        }

        case (true, false):
        {
            values[i] = (byte)(upper << 4);
            masks[i] = 0xF0;
            break;
        }

        case (false, true):
        {
            values[i] = lower;
            masks[i] = 0x0F;
            break;
        }

        case (false, false):
        {
            values[i] = 0x00;
            masks[i] = 0x00;
            break;
        }
    }
}

return (length, new(values), new(masks));

Obviously the big one is using Regex. Any ideas?
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