tests/search_test: Better documentation.

Explain which cases are covered by the test cases.  This aligns it
better with the documentation of Bsearch, and the claim about the
various ways in which it can be used.

Author: lorinder

test/search_test.c

@@ -59,7 +59,10 @@ int main(int argc, char** argv)
 #define red(x) reduce_to_bits(b, (x))
 				uint32_t d = red(rnext(&rstate));
 
-				/* Variant 1: smallest i s.t. a[i] >= key */
+				/* Variants
+				 * 1a) smallest i s.t. a[i] >= key
+				 * 1b) largest i s.t. a[i] < key (satisfied by i - 1)
+				 */
 				Bsearch(int, u, red(a[u]) < d, N, idx);
 				printf("    d = %"PRIu32" -> V1_idx = %d ", d, idx);
 				if (idx < 0 || idx > N) {
@@ -78,7 +81,10 @@ int main(int argc, char** argv)
 					return 1;
 				}
 
-				/* Variant 2: lowest i s.t. a[i] > key */
+				/* Variants
+				 * 2a) smallest i s.t. a[i] > key
+				 * 2b) largest i s.t.  a[i] <= key (satisfied by i - 1)
+				 */
 				Bsearch(int, u, red(a[u]) <= d, N, idx);
 				printf("V2_idx = %d ", idx);
 				if (idx < 0 || idx > N) {