Comment on origin of sha1 and sha224 initial values.

sha1.c

@@ -57,7 +57,7 @@ sha1_init(struct sha1_ctx *ctx)
      can initialize with a single memcpy. */
   static const uint32_t iv[_SHA1_DIGEST_LENGTH] = 
     {
-      /* SHA initial values */
+      /* SHA initial values, first 4 identical to md5's. */
       0x67452301L,
       0xEFCDAB89L,
       0x98BADCFEL,

sha256.c

@@ -129,7 +129,7 @@ sha256_digest(struct sha256_ctx *ctx,
 void
 sha224_init(struct sha256_ctx *ctx)
 {
-  /* Initial values. I's unclear how they are chosen. */
+  /* Initial values. Low 32 bits of the initial values for sha384. */
   static const uint32_t H0[_SHA256_DIGEST_LENGTH] =
   {
     0xc1059ed8, 0x367cd507, 0x3070dd17, 0xf70e5939,