Document pcu_lsb() function

While at it, fix a typo in the test output.

This function is nowadays only used in ms_current_pacch_slots(), which
is used only to print the PACCH TS (the first common UL & DL TS).

Change-Id: Id1d0b681f6866618f9f3a8c64d6a6c809ca50ea7

src/pcu_utils.h

@@ -72,6 +72,9 @@ inline unsigned int pcu_bitcount(unsigned long long x)
 	return __builtin_popcountll(x);
 }
 
+/* Trim all 1 bits except the Least Significat Bit, which is kept.
+ * equivalent of (1 << ffs(u)) / 2
+ */
 static inline uint8_t pcu_lsb(uint8_t x)
 {
 	return x & -x;

tests/types/TypesTest.cpp

@@ -937,10 +937,10 @@ static void test_lsb()
 {
 	uint8_t u = 0;
 
-	printf("Testing LBS utility...\n");
+	printf("Testing LSB utility...\n");
 
 	do {
-		uint8_t x = pcu_lsb(u); /* equivalent of (1 << ffs(u)) / 2 */
+		uint8_t x = pcu_lsb(u);
 		printf("%2X " OSMO_BIT_SPEC ": {%d} %3d\n",
 		       u, OSMO_BIT_PRINT(u), pcu_bitcount(u), x);
 		u++;

tests/types/TypesTest.ok

@@ -18,7 +18,7 @@ show_rbb: IIRRIIIR
 	06 3f 10 0d 23 6d 7f 03 18 23 00 46 a0 08 00 17 44 0b 2b 2b 2b 2b 2b 
 assignment reject: 06 3a 10 7f 06 36 14 7f 06 36 14 7f 06 36 14 7f 06 36 14 c0 2b 2b 
 assignment reject: 06 3a 10 70 06 36 14 70 06 36 14 70 06 36 14 70 06 36 14 0b 2b 2b 
-Testing LBS utility...
+Testing LSB utility...
  0 ........: {0}   0
  1 .......1: {1}   1
  2 ......1.: {1}   2