Make penalty PRNG available for general use by compiler.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/lj_jit.h b/src/lj_jit.h
index f0472282..ff3492bf 100644
--- a/src/lj_jit.h
+++ b/src/lj_jit.h
@@ -278,7 +278,7 @@ typedef struct jit_State {
 
   HotPenalty penalty[PENALTY_SLOTS];  /* Penalty slots. */
   uint32_t penaltyslot; /* Round-robin index into penalty slots. */
-  uint32_t prngstate;   /* PRNG state for penalty randomization. */
+  uint32_t prngstate;   /* PRNG state. */
 
   BPropEntry bpropcache[BPROP_SLOTS];  /* Backpropagation cache slots. */
   uint32_t bpropslot;   /* Round-robin index into bpropcache slots. */
@@ -297,6 +297,14 @@ typedef struct jit_State {
   int mcprot;           /* Protection of current mcode area. */
 } jit_State;
 
+/* Trivial PRNG e.g. used for penalty randomization. */
+static LJ_AINLINE uint32_t LJ_PRNG_BITS(jit_State *J, int bits)
+{
+  /* Yes, this LCG is very weak, but that doesn't matter for our use case. */
+  J->prngstate = J->prngstate * 1103515245 + 12345;
+  return J->prngstate >> (32-bits);
+}
+
 /* Exit stubs. */
 #if LJ_TARGET_X86ORX64
 /* Limited by the range of a short fwd jump (127): (2+2)*(32-1)-2 = 122. */