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Make Math.random() more deterministic

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This was SVN commit r7563.
This commit is contained in:
Ykkrosh
2010-05-22 00:38:33 +00:00
parent 1fc75e7605
commit 386f322b1c
6 changed files with 95 additions and 0 deletions
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source/scriptinterface/ScriptInterface.cpp
+45
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@@ -29,6 +29,9 @@
#include <boost/preprocessor/punctuation/comma_if.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>
#include <boost/random/linear_congruential.hpp>
#include <boost/random/uniform_real.hpp>
#include <boost/random/variate_generator.hpp>
#include "valgrind.h"
@@ -110,6 +113,28 @@ JSBool print(JSContext* cx, JSObject* UNUSED(obj), uintN argc, jsval* argv, jsva
return JS_TRUE;
}
// Math override functions:
JSBool Math_random(JSContext* cx, uintN UNUSED(argc), jsval* vp)
{
// Grab the RNG that was hidden in our slot
jsval rngp;
if (!JS_GetReservedSlot(cx, JSVAL_TO_OBJECT(JS_CALLEE(cx, vp)), 0, &rngp))
return JS_FALSE;
boost::rand48* rng = static_cast<boost::rand48*>(JSVAL_TO_PRIVATE(rngp));
// TODO: is the double generation sufficiently deterministic for us?
boost::uniform_real<double> dist;
boost::variate_generator<boost::rand48&, boost::uniform_real<> > gen(*rng, dist);
double r = gen();
jsval rv;
if (!JS_NewNumberValue(cx, r, &rv))
return JS_FALSE;
JS_SET_RVAL(cx, vp, rv);
return JS_TRUE;
}
} // anonymous namespace
#if ENABLE_SCRIPT_PROFILING
@@ -233,6 +258,26 @@ void* ScriptInterface::GetCallbackData(JSContext* cx)
return JS_GetContextPrivate(cx);
}
void ScriptInterface::ReplaceNondeterministicFunctions(boost::rand48& rng)
{
jsval math;
if (!JS_GetProperty(m->m_cx, m->m_glob, "Math", &math) || !JSVAL_IS_OBJECT(math))
{
LOGERROR(L"ReplaceNondeterministicFunctions: failed to get Math");
return;
}
JSFunction* random = JS_DefineFunction(m->m_cx, JSVAL_TO_OBJECT(math), "random", (JSNative)Math_random, 0,
JSPROP_ENUMERATE | JSPROP_READONLY | JSPROP_PERMANENT | JSFUN_FAST_NATIVE);
if (!random)
{
LOGERROR(L"ReplaceNondeterministicFunctions: failed to replace Math.random");
return;
}
// Store the RNG in a slot which is sort-of-guaranteed to be unused by the JS engine
JS_SetReservedSlot(m->m_cx, JS_GetFunctionObject(random), 0, PRIVATE_TO_JSVAL(&rng));
}
void ScriptInterface::Register(const char* name, JSNative fptr, size_t nargs)
{
m->Register(name, fptr, (uintN)nargs);