Special neighbor primes: Difference between revisions

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 {{libheader|ALGOL 68-primes}}
 <lang algol68>BEGIN  # find adjacent primes p1, p2 such that p1 + p2 - 1 is also prime #
-    INT max prime = 100;
-    # sieve the primes to max prime * 2 #
     PR read "primes.incl.a68" PR
-    []BOOL prime = PRIMESIEVE ( max prime * 2 );
+    INT max prime = 100;
-    # count the primes up to max prime #
+    []BOOL prime    = PRIMESIEVE ( max prime * 2 );                      # sieve the primes to max prime * 2              #
-    INT p count := 0; FOR i TO max prime DO IF prime[ i ] THEN p count +:= 1 FI OD;
+    []INT low prime = EXTRACTPRIMESUPTO max prime FROMPRIMESIEVE prime;  # construct a list of the primes up to max prime #
-    # 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;
     # find the adjacent primes p1, p2 such that p1 + p2 - 1 is prime #
     FOR i TO UPB low prime - 1 DO