RoughStrCompare

RoughStrCompare

/**
    RoughStrCompare()

    This does a rough ASCII case-insensitive string comparison.  Mainly for fun.
    All of the a-z and A-Z ASCII codes are between 0x41 - 0x5A and 0x61 - 0x7A.
    The idea here is to mask out 0x20 to make these equivalent (case-insensitive)
    but the problem with this idea is that it aliases these characters:
         @ with `    [ with {    \ with |    ] with }    ^ with ~
*/
bool RoughStrCompare(
    const char* data,       ///< Data to search
    unsigned    data_bytes, ///< Length of data in bytes
    const char* key,        ///< Key to search for
    unsigned    key_bytes); ///< Bytes in key

bool RoughStrCompare(
    const char* data,       ///< Data to search
    unsigned    data_bytes, ///< Length of data in bytes
    const char* key,        ///< Key to search for
    unsigned    key_bytes)  ///< Bytes in key
{
    // If it would be too long:
    if (key_bytes > data_bytes) {
        return false;
    }

    // Do blocks of 8 bytes
    while (key_bytes >= 8)
    {
        uint64_t a = siamese::ReadU64_LE(reinterpret_cast<const uint8_t*>(data));
        uint64_t b = siamese::ReadU64_LE(reinterpret_cast<const uint8_t*>(key));

        if (a != b)
        {
            a &= ~((a & 0x4040404040404040ULL) >> 1);
            b &= ~((b & 0x4040404040404040ULL) >> 1);
            if (a != b) {
                return false;
            }
        }

        data += 8, key += 8, key_bytes -= 8;
    }

    // Do 4 bytes
    if (key_bytes >= 4)
    {
        uint32_t a = siamese::ReadU32_LE(reinterpret_cast<const uint8_t*>(data));
        uint32_t b = siamese::ReadU32_LE(reinterpret_cast<const uint8_t*>(key));

        if (a != b)
        {
            a &= ~((a & 0x40404040) >> 1);
            b &= ~((b & 0x40404040) >> 1);
            if (a != b) {
                return false;
            }
        }

        data += 4, key += 4, key_bytes -= 4;
    }

    // Do remaining 1-3 bytes
    while (key_bytes > 0)
    {
        uint8_t a = data[0];
        uint8_t b = key[0];

        if (a != b)
        {
            a &= ~((a & 0x40) >> 1);
            b &= ~((b & 0x40) >> 1);
            if (a != b) {
                return false;
            }
        }

        ++data, ++key, --key_bytes;
    }

    return true;
}