eval: add sqrt function for computing the square root

[ffmpeg] / tests / ref / fate / h264-conformance-sharp_mp_field_1_b

0, 0, 518400, 0xc93c7c47
0, 3600, 518400, 0xa3f2e502
0, 7200, 518400, 0xb98920a4
0, 10800, 518400, 0xad098ec1
0, 14400, 518400, 0x3009b7aa
0, 18000, 518400, 0xcf514018
0, 21600, 518400, 0xd869038d
0, 25200, 518400, 0x3ce5e188
0, 28800, 518400, 0x029b4c14
0, 32400, 518400, 0xd2224afc
0, 36000, 518400, 0xbbca027c
0, 39600, 518400, 0x1f3fa0ac
0, 43200, 518400, 0x823b0125
0, 46800, 518400, 0xaaa27cfb
0, 50400, 518400, 0x5e926a4a