push

segmented.nim

@@ -0,0 +1,45 @@
+import math, sequtils
+proc simple(limit: int): seq[int] =
+  var isPrime = newSeq[bool](limit + 1)
+  for i in 0..limit:
+    isPrime[i] = true
+  isPrime[0] = false
+  isPrime[1] = false
+
+  for i in 2..int(sqrt(float(limit))):
+    if isPrime[i]:
+      var j = i * i
+      while j <= limit:
+        isPrime[j] = false
+        j += i
+
+  result = @[]
+  for i, prime in isPrime:
+    if prime:
+      result.add(i)
+
+proc segmented(L, R: int): seq[int] =
+  let limit = int(sqrt(float(R)))
+  let primes = simple(limit)
+  var isPrime = newSeq[bool](R - L + 1)
+  for i in 0..<isPrime.len:
+    isPrime[i] = true
+
+  for p in primes:
+    var start = (L div p) * p
+    if start < L: start += p
+    if start == p: start += p  
+
+    var j = start
+    while j <= R:
+      isPrime[j - L] = false
+      j += p
+
+  result = @[]
+  for i in 0..<isPrime.len:
+    if isPrime[i] and (i + L >= 2):
+      result.add(i + L)
+
+let L = 10
+let R = 500000000
+echo segmented(L, R)