REORG: tools: promote the debug PRNG to more general use as a statistical one
We frequently need to access a simple and fast PRNG for statistical
purposes. The debug_prng() function did exactly this using a xorshift
generator but its use was limited to debug only. Let's move this to
tools.h and tools.c to make it accessible everywhere. Since it needs to
be fast, its state is thread-local. An initialization function starts a
different initial value for each thread for better distribution.
diff --git a/src/debug.c b/src/debug.c
index 209199a..914c80d 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -42,16 +42,6 @@
volatile unsigned long threads_to_dump = 0;
unsigned int debug_commands_issued = 0;
-/* Xorshift RNGs from http://www.jstatsoft.org/v08/i14/paper */
-static THREAD_LOCAL unsigned int y = 2463534242U;
-static unsigned int debug_prng()
-{
- y ^= y << 13;
- y ^= y >> 17;
- y ^= y << 5;
- return y;
-}
-
/* dumps a backtrace of the current thread that is appended to buffer <buf>.
* Lines are prefixed with the string <prefix> which may be empty (used for
* indenting). It is recommended to use this at a function's tail so that
@@ -748,7 +738,7 @@
t->expire = tick_add(now_ms, inter);
/* half of the calls will wake up another entry */
- rnd = debug_prng();
+ rnd = statistical_prng();
if (rnd & 1) {
rnd >>= 1;
rnd %= tctx[0];
@@ -770,7 +760,7 @@
/* wake up two random entries */
for (i = 0; i < 2; i++) {
- rnd = debug_prng() % tctx[0];
+ rnd = statistical_prng() % tctx[0];
rnd = tctx[rnd + 2];
if (rnd & 1)