Use slice to speed up inner loop for python's nsieve benchmark (#327)

Author: bsdz

bench/algorithm/nsieve/2.py

@@ -0,0 +1,17 @@
+import sys
+
+
+def nsieve(n):
+    count = 0
+    flags = [True] * n
+    for i in range(2, n):
+        if flags[i]:
+            count += 1
+            flags[slice(i << 1, n, i)] = [False] * ((n - 1) // i - 1)
+    print(f'Primes up to {n:8} {count:8}')
+
+
+if __name__ == '__main__':
+    n = int(sys.argv[1]) if len(sys.argv) > 1 else 4
+    for i in range(0, 3):
+        nsieve(10000 << (n-i))

bench/bench_python.yaml

@@ -45,6 +45,7 @@ problems:
   - name: nsieve
     source:
       - 1.py
+      - 2.py
   - name: lru
     source:
       - 1.py