From 873455183525da257cae1da28b2959c0c409cb09 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Mon, 30 Sep 2024 09:38:34 -0700
Subject: Sieve of Eratosthenes

Really badly needs `i++` and a `for` loop
---
 .../java/com/seaofnodes/simple/Chapter15Test.java  | 49 ++++++++++++++++++++++
 1 file changed, 49 insertions(+)

(limited to 'chapter15/src')

diff --git a/chapter15/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter15/src/test/java/com/seaofnodes/simple/Chapter15Test.java
index a3dd48d0..f08abed0 100644
--- a/chapter15/src/test/java/com/seaofnodes/simple/Chapter15Test.java
+++ b/chapter15/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -70,6 +70,55 @@ return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
         assertEquals(1006L, Evaluator.evaluate(stop,  4));
     }
 
+    @Test
+    public void sieveOEratosthenes() {
+        Parser parser = new Parser(
+"""
+int[] ary = new int[arg];
+int[] primes = new int[arg];
+int nprimes = 0;
+// Find primes
+int j=2;
+while( j*j < arg ) {
+    while( ary[j]==1 ) j = j + 1;
+    // j is now a prime
+    primes[nprimes] = j;  nprimes = nprimes + 1;
+    // Mark out the rest non-primes
+    int i = j + j;
+    while( i < ary# ) {
+        ary[i] = 1;
+        i = i + j;
+    }
+    j = j + 1;
+}
+// Now just collect the remaining primes
+while( j < arg ) {
+    if( ary[j] == 0 ) {
+        primes[nprimes] = j;  nprimes = nprimes + 1;
+    }
+    j = j + 1;
+}
+// Shrink the result array to size
+int[] rez = new int[nprimes];
+j = 0;
+while( j < nprimes ) {
+    rez[j] = primes[j];
+    j = j + 1;
+}
+
+return rez;
+""");
+        StopNode stop = parser.parse(false).iterate(true);
+        assertEquals("return []int;", stop.toString());
+        Evaluator.Obj obj = (Evaluator.Obj)Evaluator.evaluate(stop, 20);
+        assertEquals("[]int {\n  # :int;\n  [] :int;\n}",obj.struct().toString());
+        long nprimes = (Long)obj.fields()[0];
+        long[] primes = new long[]{2,3,5,7,11,13,17,19};
+        for( int i=0; i<nprimes; i++ )
+            assertEquals(primes[i],(long)(Long)obj.fields()[i+1]);
+    }
+
+
     @Test
     public void testBad0() {
         Parser parser = new Parser(
-- 
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