Talk:ALGOL 68-primes
Source code
<lang algol68># primes.incl.a68: prime related operators, procedure etc. #
# returns a sieve of primes up to n # OP PRIMESIEVE = ( INT n )[]BOOL: BEGIN [ 0 : n ]BOOL prime; prime[ 0 ] := prime[ 1 ] := FALSE; prime[ 2 ] := TRUE; FOR i FROM 3 BY 2 TO UPB prime DO prime[ i ] := TRUE OD; FOR i FROM 4 BY 2 TO UPB prime DO prime[ i ] := FALSE OD; FOR i FROM 3 BY 2 TO ENTIER sqrt( UPB prime ) DO IF prime[ i ] THEN FOR s FROM i * i BY i + i TO UPB prime DO prime[ s ] := FALSE OD FI OD; prime END; # PRIMESIEVE #
# modes and operators for extracting primes from a sieve #
INT first n primes extract op = 0; INT primes up to extract op = 1;
MODE PRIMEEXTRACT = STRUCT( INT extract op, INT n );
# returns a PRIMEEXTRACT with the first n primces extract op # OP EXTRACTFIRST = ( INT n )PRIMEEXTRACT: PRIMEEXTRACT( first n primes extract op, n );
# returns a PRIMEEXTRACT with primes up to extract op # OP EXTRACTPRIMESUPTO = ( INT n )PRIMEEXTRACT: PRIMEEXTRACT( primes up to extract op, n );
# returns an array of primes extracted from prime # # as specified by by the extract op and number of primes in ex # PRIO PRIMESFROMSIEVE = 9, FROMPRIMESIEVE = 9; OP PRIMESFROMSIEVE = ( PRIMEEXTRACT ex, []BOOL prime )[]INT: IF extract op OF ex = first n primes extract op THEN # extract the first n OF ex primes # # count the primes up n OF ex # INT p count := 0; FOR i TO UPB prime WHILE p count < n OF ex DO IF prime[ i ] THEN p count +:= 1 FI OD; # construct a list of the first n OF ex primes or p count, # # whichever is smaller # [ 1 : p count ]INT low prime; INT low pos := 0; FOR i WHILE low pos < UPB low prime DO IF prime[ i ] THEN low prime[ low pos +:= 1 ] := i FI OD; low prime ELSE # extract primes up to n OF ex primes # INT max prime = n OF ex; # count the primes up to max prime # INT p count := 0; FOR i TO max prime DO IF prime[ i ] THEN p count +:= 1 FI OD; # construct a list of the primes up to max prime # [ 1 : p count ]INT low prime; INT low pos := 0; FOR i WHILE low pos < UPB low prime DO IF prime[ i ] THEN low prime[ low pos +:= 1 ] := i FI OD; low prime FI # PRIMESFROMSIEVE # ; # alternative spelling of the operator name # OP FROMPRIMESIEVE = ( PRIMEEXTRACT ex, []BOOL prime )[]INT: ex PRIMESFROMSIEVE prime;
- END primes.incl.a68 #</lang>