Created
August 26, 2012 15:57
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#include <stdint.h> | |
const uint16_t squares[] = { | |
0, 1, 4, 9, | |
16, 25, 36, 49, | |
64, 81, 100, 121, | |
144, 169, 196, 225, | |
256, 289, 324, 361, | |
400, 441, 484, 529, | |
576, 625, 676, 729, | |
784, 841, 900, 961, | |
1024, 1089, 1156, 1225, | |
1296, 1369, 1444, 1521, | |
1600, 1681, 1764, 1849, | |
1936, 2025, 2116, 2209, | |
2304, 2401, 2500, 2601, | |
2704, 2809, 2916, 3025, | |
3136, 3249, 3364, 3481, | |
3600, 3721, 3844, 3969, | |
4096, 4225, 4356, 4489, | |
4624, 4761, 4900, 5041, | |
5184, 5329, 5476, 5625, | |
5776, 5929, 6084, 6241, | |
6400, 6561, 6724, 6889, | |
7056, 7225, 7396, 7569, | |
7744, 7921, 8100, 8281, | |
8464, 8649, 8836, 9025, | |
9216, 9409, 9604, 9801, | |
10000, 10201, 10404, 10609, | |
10816, 11025, 11236, 11449, | |
11664, 11881, 12100, 12321, | |
12544, 12769, 12996, 13225, | |
13456, 13689, 13924, 14161, | |
14400, 14641, 14884, 15129, | |
15376, 15625, 15876, 16129, | |
16384, 16641, 16900, 17161, | |
17424, 17689, 17956, 18225, | |
18496, 18769, 19044, 19321, | |
19600, 19881, 20164, 20449, | |
20736, 21025, 21316, 21609, | |
21904, 22201, 22500, 22801, | |
23104, 23409, 23716, 24025, | |
24336, 24649, 24964, 25281, | |
25600, 25921, 26244, 26569, | |
26896, 27225, 27556, 27889, | |
28224, 28561, 28900, 29241, | |
29584, 29929, 30276, 30625, | |
30976, 31329, 31684, 32041, | |
32400, 32761, 33124, 33489, | |
33856, 34225, 34596, 34969, | |
35344, 35721, 36100, 36481, | |
36864, 37249, 37636, 38025, | |
38416, 38809, 39204, 39601, | |
40000, 40401, 40804, 41209, | |
41616, 42025, 42436, 42849, | |
43264, 43681, 44100, 44521, | |
44944, 45369, 45796, 46225, | |
46656, 47089, 47524, 47961, | |
48400, 48841, 49284, 49729, | |
50176, 50625, 51076, 51529, | |
51984, 52441, 52900, 53361, | |
53824, 54289, 54756, 55225, | |
55696, 56169, 56644, 57121, | |
57600, 58081, 58564, 59049, | |
59536, 60025, 60516, 61009, | |
61504, 62001, 62500, 63001, | |
63504, 64009, 64516, 65025 | |
}; | |
inline int isqrt(uint16_t x) { | |
int mid = 128; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 64; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 32; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 16; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 8; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 4; | |
mid += ((squares[mid] < x) - (x < squares[mid])) * 2; | |
mid += ((squares[mid] < x) - (x < squares[mid])); | |
mid -= x < squares[mid]; | |
return mid; | |
} | |
/* this version is a lot faster */ | |
int isqrt_with_branch(uint16_t x) { | |
int low = 0; | |
int high = 255; | |
int i; | |
while (low <= high) { | |
int mid = (low + high) / 2; | |
if (x < squares[mid]) { | |
high = mid - 1; | |
} else if (squares[mid] < x) { | |
low = mid + 1; | |
} else { | |
return mid; | |
} | |
} | |
return high; | |
} |
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