(perl #127663) create a separate random souce for internal use

and use it to initialize hash randomization and to innoculate against
quadratic behaviour in pp_sort

embedvar.h

@@ -173,6 +173,7 @@
 #define PL_incgv		(vTHX->Iincgv)
 #define PL_initav		(vTHX->Iinitav)
 #define PL_inplace		(vTHX->Iinplace)
+#define PL_internal_random_state	(vTHX->Iinternal_random_state)
 #define PL_isarev		(vTHX->Iisarev)
 #define PL_known_layers		(vTHX->Iknown_layers)
 #define PL_last_in_gv		(vTHX->Ilast_in_gv)

intrpvar.h

@@ -810,6 +810,14 @@ PERLVAR(I, random_state, PL_RANDOM_STATE_TYPE)
 
 PERLVARI(I, dump_re_max_len, STRLEN, 0)
 
+/* For internal uses of randomness, this ensures the sequence of
+ * random numbers returned by rand() isn't modified by perl's internal
+ * use of randomness.
+ * This is important if the user has called srand() with a seed.
+ */
+
+PERLVAR(I, internal_random_state, PL_RANDOM_STATE_TYPE)
+
 /* If you are adding a U8 or U16, check to see if there are 'Space' comments
  * above on where there are gaps which currently will be structure padding.  */
 

perl.c

@@ -261,6 +261,8 @@ perl_construct(pTHXx)
 
     init_constants();
 
+    Perl_drand48_init_r(&PL_internal_random_state, seed());
+
     SvREADONLY_on(&PL_sv_placeholder);
     SvREFCNT(&PL_sv_placeholder) = SvREFCNT_IMMORTAL;
 

pp_sort.c

@@ -787,7 +787,7 @@ S_qsortsvu(pTHX_ SV ** array, size_t num_elts, SVCOMPARE_t compare)
       size_t n;
       SV ** const q = array;
       for (n = num_elts; n > 1; ) {
-         const size_t j = (size_t)(n-- * Drand01());
+         const size_t j = (size_t)(n-- * Perl_internal_drand48());
          temp = q[j];
          q[j] = q[n];
          q[n] = temp;

util.c

@@ -4757,10 +4757,8 @@ Perl_get_hash_seed(pTHX_ unsigned char * const seed_buffer)
     else
 #endif
     {
-        (void)seedDrand01((Rand_seed_t)seed());
-
         for( i = 0; i < PERL_HASH_SEED_BYTES; i++ ) {
-            seed_buffer[i] = (unsigned char)(Drand01() * (U8_MAX+1));
+            seed_buffer[i] = (unsigned char)(Perl_internal_drand48() * (U8_MAX+1));
         }
     }
 #ifdef USE_PERL_PERTURB_KEYS

util.h

@@ -85,6 +85,12 @@ typedef struct PERL_DRAND48_T perl_drand48_t;
 #define Perl_drand48_init(seed) (Perl_drand48_init_r(&PL_random_state, (seed)))
 #define Perl_drand48() (Perl_drand48_r(&PL_random_state))
 
+#ifdef PERL_CORE
+/* uses a different source of randomness to avoid interfering with the results
+ * of rand() */
+#define Perl_internal_drand48() (Perl_drand48_r(&PL_internal_random_state))
+#endif
+
 #ifdef USE_C_BACKTRACE
 
 typedef struct {