From: Ben Pfaff <blp@cs.stanford.edu>
Date: Fri, 3 Sep 2004 06:33:35 +0000 (+0000)
Subject: Comments.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=commitdiff_plain;h=649df740b717000030c27d70209f4491da3a63f9

Comments.
---

diff --git a/src/lib/random.c b/src/lib/random.c
index 3fcf62d..63d798d 100644
--- a/src/lib/random.c
+++ b/src/lib/random.c
@@ -3,11 +3,24 @@
 #include <stdint.h>
 #include "debug.h"
 
-/* RC4-based pseudo-random state. */
-static uint8_t s[256];
-static uint8_t s_i, s_j;
-static bool inited;
+/* RC4-based pseudo-random number generator (PRNG).
 
+   RC4 is a stream cipher.  We're not using it here for its
+   cryptographic properties, but because it is easy to implement
+   and its output is plenty random for non-cryptographic
+   purposes.
+
+   See http://en.wikipedia.org/wiki/RC4_(cipher) for information
+   on RC4.*/
+
+/* RC4 state. */
+static uint8_t s[256];          /* S[]. */
+static uint8_t s_i, s_j;        /* i, j. */
+
+/* Already initialized? */
+static bool inited;     
+
+/* Swaps the bytes pointed to by A and B. */
 static inline void
 swap_byte (uint8_t *a, uint8_t *b) 
 {
@@ -16,6 +29,8 @@ swap_byte (uint8_t *a, uint8_t *b)
   *b = t;
 }
 
+/* Initializes the PRNG with the given SEED.
+   Does nothing if the PRNG has already been initialized. */
 void
 random_init (unsigned seed)
 {
@@ -38,6 +53,7 @@ random_init (unsigned seed)
   inited = true;
 }
 
+/* Writes SIZE random bytes into BUF. */
 void
 random_bytes (void *buf_, size_t size) 
 {