src/part1/examples/repo/charlie/sqrtlib/isqrt_unroll.c

unsigned int isqrt( unsigned long x ) {
    static const unsigned char sqq_table[] = {
       0,  16,  22,  27,  32,  35,  39,  42,  45,  48,  50,  53,  55,  57,
      59,  61,  64,  65,  67,  69,  71,  73,  75,  76,  78,  80,  81,  83,
      84,  86,  87,  89,  90,  91,  93,  94,  96,  97,  98,  99, 101, 102,
     103, 104, 106, 107, 108, 109, 110, 112, 113, 114, 115, 116, 117, 118,
     119, 120, 121, 122, 123, 124, 125, 126, 128, 128, 129, 130, 131, 132,
     133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 144, 145,
     146, 147, 148, 149, 150, 150, 151, 152, 153, 154, 155, 155, 156, 157,
     158, 159, 160, 160, 161, 162, 163, 163, 164, 165, 166, 167, 167, 168,
     169, 170, 170, 171, 172, 173, 173, 174, 175, 176, 176, 177, 178, 178,
     179, 180, 181, 181, 182, 183, 183, 184, 185, 185, 186, 187, 187, 188,
     189, 189, 190, 191, 192, 192, 193, 193, 194, 195, 195, 196, 197, 197,
     198, 199, 199, 200, 201, 201, 202, 203, 203, 204, 204, 205, 206, 206,
     207, 208, 208, 209, 209, 210, 211, 211, 212, 212, 213, 214, 214, 215,
     215, 216, 217, 217, 218, 218, 219, 219, 220, 221, 221, 222, 222, 223,
     224, 224, 225, 225, 226, 226, 227, 227, 228, 229, 229, 230, 230, 231,
     231, 232, 232, 233, 234, 234, 235, 235, 236, 236, 237, 237, 238, 238,
     239, 240, 240, 241, 241, 242, 242, 243, 243, 244, 244, 245, 245, 246,
     246, 247, 247, 248, 248, 249, 249, 250, 250, 251, 251, 252, 252, 253,
     253, 254, 254, 255
    };

    unsigned long xn;

    if (x >= 0x10000)
        if (x >= 0x1000000)
            if (x >= 0x10000000)
                if (x >= 0x40000000) {
                    if (x >= 65535UL*65535UL)
                        return 65535;
                    xn = sqq_table[x>>24] << 8;
                } else
                    xn = sqq_table[x>>22] << 7;
            else
                if (x >= 0x4000000)
                    xn = sqq_table[x>>20] << 6;
                else
                    xn = sqq_table[x>>18] << 5;
        else {
            if (x >= 0x100000)
                if (x >= 0x400000)
                    xn = sqq_table[x>>16] << 4;
                else
                    xn = sqq_table[x>>14] << 3;
            else
                if (x >= 0x40000)
                    xn = sqq_table[x>>12] << 2;
                else
                    xn = sqq_table[x>>10] << 1;

            goto nr1;
        }
    else
        if (x >= 0x100) {
            if (x >= 0x1000)
                if (x >= 0x4000)
                    xn = (sqq_table[x>>8] >> 0) + 1;
                else
                    xn = (sqq_table[x>>6] >> 1) + 1;
            else
                if (x >= 0x400)
                    xn = (sqq_table[x>>4] >> 2) + 1;
                else
                    xn = (sqq_table[x>>2] >> 3) + 1;

            goto adj;
        } else
            return sqq_table[x] >> 4;

    xn = (xn + 1 + x / xn) / 2;
nr1:
    xn = (xn + 1 + x / xn) / 2;
adj:

    if (xn * xn > x)
       xn--;

    return xn;
}