- tb_uint32_t tb_isqrti(tb_uint32_t x)
- {
- static tb_uint8_t const table[256] =
- {
- 0, 16, 23, 28, 32, 36, 40, 43, 46, 48, 51, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 77, 79, 80, 82, 84, 85, 87, 88, 90
- , 91, 92, 94, 95, 96, 98, 99, 100, 102, 103, 104, 105, 107, 108, 109, 110, 111, 112, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127
- , 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 144, 145, 146, 147, 148, 149, 150, 151, 151, 152, 153, 154, 155, 156, 156
- , 157, 158, 159, 160, 160, 161, 162, 163, 164, 164, 165, 166, 167, 168, 168, 169, 170, 171, 171, 172, 173, 174, 174, 175, 176, 176, 177, 178, 179, 179, 180, 181
- , 182, 182, 183, 184, 184, 185, 186, 186, 187, 188, 188, 189, 190, 190, 191, 192, 192, 193, 194, 194, 195, 196, 196, 197, 198, 198, 199, 200, 200, 201, 202, 202
- , 203, 204, 204, 205, 205, 206, 207, 207, 208, 208, 209, 210, 210, 211, 212, 212, 213, 213, 214, 215, 215, 216, 216, 217, 218, 218, 219, 219, 220, 220, 221, 222
- , 222, 223, 223, 224, 224, 225, 226, 226, 227, 227, 228, 228, 229, 230, 230, 231, 231, 232, 232, 233, 233, 234, 235, 235, 236, 236, 237, 237, 238, 238, 239, 239
- , 240, 240, 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, 255, 255
- };
- tb_size_t b = 0;
- if (x < 255) return (table[x + 1] - 1) >> 4;
- else if (x < (1 << 12)) b = table[x >> 4] >> 2;
- else if (x < (1 << 14)) b = table[x >> 6] >> 1;
- else if (x < (1 << 16)) b = table[x >> 8];
- else
- {
- tb_size_t s = tb_ilog2i(x >> 16) >> 1;
- tb_size_t c = x >> (s + 2);
- b = table[c >> (s + 8)];
- b = tb_idivi8(c, (tb_uint8_t)b) + (b << s);
- }
- return b - (x < b * b);
- }
- //该片段来自于http://www.codesnippet.cn/detail/1912201411358.html
来源: http://www.codesnippet.cn/detail/1912201411358.html