From: W. Trevor King <wking@drexel.edu>
Date: Sat, 30 Oct 2010 19:52:19 +0000 (-0400)
Subject: Add explanatory comment and clean up src/global_operations/print_tree.c output.
X-Git-Url: http://git.tremily.us/?a=commitdiff_plain;h=708a51f60c4551308a1c1a0f5cbfd507c4aef0fd;p=parallel_computing.git

Add explanatory comment and clean up src/global_operations/print_tree.c output.
---

diff --git a/src/global_operations/print_tree.c b/src/global_operations/print_tree.c
index f7383cd..b5510f2 100644
--- a/src/global_operations/print_tree.c
+++ b/src/global_operations/print_tree.c
@@ -2,10 +2,24 @@
 
 #include <stdio.h>
 #include <math.h>
+
+/* tree broadcast routine:
+ * 0 -(gen=1)-> 1
+ *
+ * 0 -(gen=2)-> 2
+ * 1 -(gen=2)-> 3
+ *
+ * 0 -(gen=4)-> 4
+ * 1 -(gen=4)-> 5
+ * 2 -(gen=4)-> 6
+ * 3 -(gen=4)-> 7
+ * ...
+ *
+ * In gen, processes (gen <= rank < 2*gen) will receive the broadcast data.
+ */
 int main(int argc, char *argv[])
 {
-	int two_to_generation;
-	int rank, size;
+	int gen, rank, size;
 	int to, from;
 
 	/* scan over a hypothetical virtual machine of 15 nodes */
@@ -13,25 +27,20 @@ int main(int argc, char *argv[])
 	for (rank = 0; rank < size; rank++) {
 		printf("rank %d", rank);
 
-		/* two_to_generation reflects the steps in the tree broadcast */
-		two_to_generation = 1;
-		while (two_to_generation < size) {
-
-			/* receive message */
-			if (rank >= two_to_generation
-			    && rank < two_to_generation * 2) {
-				from = rank - two_to_generation;
-				if (from < size)
-					printf(" -- from %d", from);
-			}
-
-			/* send message */
-			if (rank < two_to_generation) {
-				to = rank + two_to_generation;
+		/* gen reflects the generation (depth) in the tree broadcast */
+		gen = 1;
+		while (gen < size) {
+			if (rank >= 2 * gen) {	/* wait for the data to come out */
+				printf("\t");
+			} else if (rank >= gen && rank < 2 * gen) {	/* receive message */
+				from = rank - gen;
+				printf("\tfrom %d", from);
+			} else if (rank < gen) {	/* send message */
+				to = rank + gen;
 				if (to < size)
-					printf(" -- to %d", to);
+					printf("\tto %d", to);
 			}
-			two_to_generation = 2 * two_to_generation;
+			gen *= 2;
 		}
 
 		/* done for a given rank */