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Fast primality for 32 bit integers, using a single SPRP test
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""" BBerg32 | |
Primality test for 32 bit integers using a single SPRP test. | |
The SPRP base comes from a hash table. | |
Hash and bases by Bradley Berg | |
See https://techneon.com/download/is.prime.32.base.data | |
""" | |
bases = [ | |
1216, 1836, 8885, 4564, 10978, 5228, 15613, 13941, | |
1553, 173, 3615, 3144, 10065, 9259, 233, 2362, | |
6244, 6431, 10863, 5920, 6408, 6841, 22124, 2290, | |
45597, 6935, 4835, 7652, 1051, 445, 5807, 842, | |
1534, 22140, 1282, 1733, 347, 6311, 14081, 11157, | |
186, 703, 9862, 15490, 1720, 17816, 10433, 49185, | |
2535, 9158, 2143, 2840, 664, 29074, 24924, 1035, | |
41482, 1065, 10189, 8417, 130, 4551, 5159, 48886, | |
786, 1938, 1013, 2139, 7171, 2143, 16873, 188, | |
5555, 42007, 1045, 3891, 2853, 23642, 148, 3585, | |
3027, 280, 3101, 9918, 6452, 2716, 855, 990, | |
1925, 13557, 1063, 6916, 4965, 4380, 587, 3214, | |
1808, 1036, 6356, 8191, 6783, 14424, 6929, 1002, | |
840, 422, 44215, 7753, 5799, 3415, 231, 2013, | |
8895, 2081, 883, 3855, 5577, 876, 3574, 1925, | |
1192, 865, 7376, 12254, 5952, 2516, 20463, 186, | |
5411, 35353, 50898, 1084, 2127, 4305, 115, 7821, | |
1265, 16169, 1705, 1857, 24938, 220, 3650, 1057, | |
482, 1690, 2718, 4309, 7496, 1515, 7972, 3763, | |
10954, 2817, 3430, 1423, 714, 6734, 328, 2581, | |
2580, 10047, 2797, 155, 5951, 3817, 54850, 2173, | |
1318, 246, 1807, 2958, 2697, 337, 4871, 2439, | |
736, 37112, 1226, 527, 7531, 5418, 7242, 2421, | |
16135, 7015, 8432, 2605, 5638, 5161, 11515, 14949, | |
748, 5003, 9048, 4679, 1915, 7652, 9657, 660, | |
3054, 15469, 2910, 775, 14106, 1749, 136, 2673, | |
61814, 5633, 1244, 2567, 4989, 1637, 1273, 11423, | |
7974, 7509, 6061, 531, 6608, 1088, 1627, 160, | |
6416, 11350, 921, 306, 18117, 1238, 463, 1722, | |
996, 3866, 6576, 6055, 130, 24080, 7331, 3922, | |
8632, 2706, 24108, 32374, 4237, 15302, 287, 2296, | |
1220, 20922, 3350, 2089, 562, 11745, 163, 11951, | |
] | |
# Strong probable prime to base a | |
def is_sprp(n, a): | |
m = n - 1 | |
s = (m & -m).bit_length() - 1 | |
x = pow(a, m >> s, n) | |
if x == 1 or x == m: | |
return True | |
for _ in range(s - 1): | |
x = x * x % n | |
if x == 1: | |
#previous (x+1)(x-1) == 0 mod n | |
return False | |
if x == m: | |
return True | |
return False | |
def is_prime_BBerg32(x): | |
for p in (2, 3, 5, 7): | |
if x % p == 0: | |
return x == p | |
if x < 121: return x > 1 | |
h = x * 0xAD625B89 >> 24 & 0xff | |
return is_sprp(x, bases[h]) | |
# Test | |
s = 2 + sum(i for i in range(3, 10000, 2) if is_prime_BBerg32(i)) | |
print(s) | |
# 5736396 |
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A slightly more efficient version (the SPRP test is inlined), with a more extensive demo, with timing, on SageMathCell. The SPRP bases are encoded using a85encode.