Miika Alonen
5d122a90e0
Syntax for monzos supported in scala scales: [-1 1> etc.
Support for escaped pitches: {q12 e23 26}
36 lines
1.3 KiB
Python
36 lines
1.3 KiB
Python
"""Collection of generators"""
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# Sieve of Eratosthenes
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# Based on code by David Eppstein, UC Irvine, 28 Feb 2002
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# http://code.activestate.com/recipes/117119/
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def gen_primes():
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"""Generate an infinite sequence of prime numbers."""
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# Maps composites to primes witnessing their compositeness.
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# This is memory efficient, as the sieve is not "run forward"
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# indefinitely, but only as long as required by the current
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# number being tested.
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sieve = {}
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# The running integer that's checked for primeness
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current = 2
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while True:
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if current not in sieve:
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# current is a new prime.
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# Yield it and mark its first multiple that isn't
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# already marked in previous iterations
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yield current
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sieve[current * current] = [current]
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else:
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# current is composite. sieve[current] is the list of primes that
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# divide it. Since we've reached current, we no longer
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# need it in the map, but we'll mark the next
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# multiples of its witnesses to prepare for larger
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# numbers
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for composite in sieve[current]:
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sieve.setdefault(composite + current, []).append(composite)
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del sieve[current]
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current += 1
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