Parallel calculations: Difference between revisions

Content added Content deleted

Inline

@@ Line 1,228: / Line 1,228: @@
 =={{header|Nim}}==
+===Using threads===
 We use one thread per number to process. To find the lowest prime factor, we use a simple algorithm as performance is not important here.
@@ Line 1,300: / Line 1,301: @@
 The first number with the largest minimum prime factor is: 115797840077099
 Its factors are: 544651, 212609249</pre>
+===Using parallel statement===
+The parallel statement is an experimental feature. It uses threads but may simplify slightly the code in comparison to manual management.
+Note that program must be compiled with option <code>--threads:on</code>.
+<lang Nim>import sequtils, strutils, threadpool
+{.experimental: "parallel".}
+const Numbers = [576460752303423487,
+                 576460752303423487,
+                 576460752303423487,
+                 112272537195293,
+                 115284584522153,
+                 115280098190773,
+                 115797840077099,
+                 112582718962171,
+                 299866111963290359]
+proc lowestFactor(n: int64): int64 =
+  if n mod 2 == 0: return 2
+  if n mod 3 == 0: return 3
+  var p = 5
+  var delta = 2
+  while p * p < n:
+    if n mod p == 0: return p
+    inc p, delta
+    delta = 6 - delta
+  result = n
+proc factors(n, lowest: int64): seq[int64] =
+  var n = n
+  var lowest = lowest
+  while true:
+    result.add lowest
+    n = n div lowest
+    if n == 1: break
+    lowest = lowestFactor(n)
+# Launch the threads.
+var results: array[Numbers.len, int64]    # To store the results.
+parallel:
+  for i, n in Numbers:
+    results[i] = spawn lowestFactor(n)
+# Find the minimum prime factor and the first number with this minimum factor.
+let maxIdx = results.maxIndex()
+let maxMinfact = results[maxIdx]
+let result = Numbers[maxIdx]
+echo ""
+echo "The first number with the largest minimum prime factor is: ", result
+echo "Its factors are: ", result.factors(maxMinfact).join(", ")</lang>
+{{out}}
+Output is the same as with manual management of threads.
 =={{header|Oforth}}==