diff --git a/js/src/jscntxt.cpp b/js/src/jscntxt.cpp
index 97b5d60abfd..ce93c37c36e 100644
--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -58,6 +58,7 @@
 #include "jsfun.h"
 #include "jsgc.h"
 #include "jslock.h"
+#include "jsmath.h"
 #include "jsnum.h"
 #include "jsobj.h"
 #include "jsopcode.h"
@@ -83,6 +84,7 @@ InitThreadData(JSThreadData *data)
 #ifdef JS_TRACER
     js_InitJIT(&data->traceMonitor);
 #endif
+    js_InitRandom(data);
 }
 
 static void
diff --git a/js/src/jscntxt.h b/js/src/jscntxt.h
index af79b64bd3e..0a24cd140e0 100644
--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -250,6 +250,9 @@ struct JSThreadData {
     /* Property cache for faster call/get/set invocation. */
     JSPropertyCache     propertyCache;
 
+    /* Random number generator state, used by jsmath.cpp. */
+    int64               rngSeed;
+
 #ifdef JS_TRACER
     /* Trace-tree JIT recorder/interpreter state. */
     JSTraceMonitor      traceMonitor;
@@ -456,14 +459,6 @@ struct JSRuntime {
      */
     JSSetSlotRequest    *setSlotRequests;
 
-    /* Random number generator state, used by jsmath.c. */
-    JSBool              rngInitialized;
-    int64               rngMultiplier;
-    int64               rngAddend;
-    int64               rngMask;
-    int64               rngSeed;
-    jsdouble            rngDscale;
-
     /* Well-known numbers held for use by this runtime's contexts. */
     jsdouble            *jsNaN;
     jsdouble            *jsNegativeInfinity;
diff --git a/js/src/jsmath.cpp b/js/src/jsmath.cpp
index dd6fd51665c..cd805f18cab 100644
--- a/js/src/jsmath.cpp
+++ b/js/src/jsmath.cpp
@@ -427,90 +427,47 @@ math_pow(JSContext *cx, uintN argc, jsval *vp)
     return js_NewNumberInRootedValue(cx, z, vp);
 }
 
+static const int64 RNG_MULTIPLIER = 0x5DEECE66DLL;
+static const int64 RNG_ADDEND = 0xBLL;
+static const int64 RNG_MASK = (1LL << 48) - 1;
+static const jsdouble RNG_DSCALE = jsdouble(1LL << 53);
+
 /*
  * Math.random() support, lifted from java.util.Random.java.
  */
-static void
-random_setSeed(JSRuntime *rt, int64 seed)
+static inline void
+random_setSeed(JSThreadData *data, int64 seed)
 {
-    int64 tmp;
-
-    JSLL_I2L(tmp, 1000);
-    JSLL_DIV(seed, seed, tmp);
-    JSLL_XOR(tmp, seed, rt->rngMultiplier);
-    JSLL_AND(rt->rngSeed, tmp, rt->rngMask);
+    data->rngSeed = (seed ^ RNG_MULTIPLIER) & RNG_MASK;
 }
 
 void
-js_random_init(JSRuntime *rt)
+js_InitRandom(JSThreadData *data)
 {
-    int64 tmp, tmp2;
-
-    /* Do at most once. */
-    if (rt->rngInitialized)
-        return;
-    rt->rngInitialized = JS_TRUE;
-
-    /* rt->rngMultiplier = 0x5DEECE66DL */
-    JSLL_ISHL(tmp, 0x5, 32);
-    JSLL_UI2L(tmp2, 0xDEECE66DL);
-    JSLL_OR(rt->rngMultiplier, tmp, tmp2);
-
-    /* rt->rngAddend = 0xBL */
-    JSLL_I2L(rt->rngAddend, 0xBL);
-
-    /* rt->rngMask = (1L << 48) - 1 */
-    JSLL_I2L(tmp, 1);
-    JSLL_SHL(tmp2, tmp, 48);
-    JSLL_SUB(rt->rngMask, tmp2, tmp);
-
-    /* rt->rngDscale = (jsdouble)(1L << 53) */
-    JSLL_SHL(tmp2, tmp, 53);
-    JSLL_L2D(rt->rngDscale, tmp2);
-
     /* Finally, set the seed from current time. */
-    random_setSeed(rt, PRMJ_Now());
+    random_setSeed(data, PRMJ_Now() / 1000);
 }
 
-static uint32
-random_next(JSRuntime *rt, int bits)
+static inline uint64
+random_next(JSThreadData *data, int bits)
 {
-    int64 nextseed, tmp;
-    uint32 retval;
-
-    JSLL_MUL(nextseed, rt->rngSeed, rt->rngMultiplier);
-    JSLL_ADD(nextseed, nextseed, rt->rngAddend);
-    JSLL_AND(nextseed, nextseed, rt->rngMask);
-    rt->rngSeed = nextseed;
-    JSLL_USHR(tmp, nextseed, 48 - bits);
-    JSLL_L2I(retval, tmp);
-    return retval;
+    uint64 nextseed = data->rngSeed * RNG_MULTIPLIER;
+    nextseed += RNG_ADDEND;
+    nextseed &= RNG_MASK;
+    data->rngSeed = nextseed;
+    return nextseed >> (48 - bits);
 }
 
-jsdouble
-js_random_nextDouble(JSRuntime *rt)
+static inline jsdouble
+random_nextDouble(JSThreadData *data)
 {
-    int64 tmp, tmp2;
-    jsdouble d;
-
-    JSLL_ISHL(tmp, random_next(rt, 26), 27);
-    JSLL_UI2L(tmp2, random_next(rt, 27));
-    JSLL_ADD(tmp, tmp, tmp2);
-    JSLL_L2D(d, tmp);
-    return d / rt->rngDscale;
+    return jsdouble((random_next(data, 26) << 27) + random_next(data, 27)) / RNG_DSCALE;
 }
 
 static JSBool
 math_random(JSContext *cx, uintN argc, jsval *vp)
 {
-    JSRuntime *rt;
-    jsdouble z;
-
-    rt = cx->runtime;
-    JS_LOCK_RUNTIME(rt);
-    js_random_init(rt);
-    z = js_random_nextDouble(rt);
-    JS_UNLOCK_RUNTIME(rt);
+    jsdouble z = random_nextDouble(JS_THREAD_DATA(cx));
     return js_NewNumberInRootedValue(cx, z, vp);
 }
 
@@ -716,13 +673,9 @@ math_pow_tn(jsdouble d, jsdouble p)
 }
 
 static jsdouble FASTCALL
-math_random_tn(JSRuntime* rt)
+math_random_tn(JSContext *cx)
 {
-    JS_LOCK_RUNTIME(rt);
-    js_random_init(rt);
-    jsdouble z = js_random_nextDouble(rt);
-    JS_UNLOCK_RUNTIME(rt);
-    return z;
+    return random_nextDouble(JS_THREAD_DATA(cx));
 }
 
 static jsdouble FASTCALL
@@ -752,7 +705,7 @@ JS_DEFINE_TRCINFO_1(math_min,
 JS_DEFINE_TRCINFO_1(math_pow,
     (2, (static, DOUBLE, math_pow_tn, DOUBLE, DOUBLE,   1, 1)))
 JS_DEFINE_TRCINFO_1(math_random,
-    (1, (static, DOUBLE, math_random_tn, RUNTIME,       0, 0)))
+    (1, (static, DOUBLE, math_random_tn, CONTEXT,       0, 0)))
 JS_DEFINE_TRCINFO_1(math_round,
     (1, (static, DOUBLE, math_round_tn, DOUBLE,         1, 1)))
 JS_DEFINE_TRCINFO_1(math_ceil,
diff --git a/js/src/jsmath.h b/js/src/jsmath.h
index 63c8741945e..d6c67814374 100644
--- a/js/src/jsmath.h
+++ b/js/src/jsmath.h
@@ -51,10 +51,7 @@ extern JSObject *
 js_InitMathClass(JSContext *cx, JSObject *obj);
 
 extern void
-js_random_init(JSRuntime *rt);
-
-extern jsdouble
-js_random_nextDouble(JSRuntime *rt);
+js_InitRandom(JSThreadData *data);
 
 JS_END_EXTERN_C