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Fix floating-point constant precision in compiled kernels #4511

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Fix floating-point constant precision in compiled kernels #4511

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e834c7b
Fix precision of constants in compiled kernels
Ryan11c Sep 15, 2026
da7f88b
Add tests for compiled constant precision
Ryan11c Sep 15, 2026
7a74063
Align float precision test with issue
Ryan11c Sep 15, 2026
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4 changes: 2 additions & 2 deletions mlx/backend/common/compiled.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,9 +37,9 @@ void print_float_constant(std::ostream& os, const array& x) {

auto old_precision = os.precision();
if constexpr (std::is_same_v<T, double>) {
os << std::setprecision(std::numeric_limits<double>::digits10 + 1);
os << std::setprecision(std::numeric_limits<double>::max_digits10);
} else {
os << std::setprecision(std::numeric_limits<float>::digits10 + 1);
os << std::setprecision(std::numeric_limits<float>::max_digits10);
}
os << value << std::setprecision(old_precision);
}
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15 changes: 10 additions & 5 deletions python/tests/test_compile.py
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Expand Up @@ -87,6 +87,12 @@ def test_compile_nonfinite_constants(self):
self.assertEqual(out[0].item(), 1.0)
self.assertEqual(out[1].item(), float("-inf"))

def test_compile_float_constant_precision(self):
x = mx.ones((4,), dtype=mx.float32)
for constant in (1 / 3, 128**-0.5, 0.7071067811865476):
fun = lambda x, constant=constant: (x * x) * constant
self.assertTrue(mx.array_equal(mx.compile(fun)(x), fun(x)))

def test_compile_tuple_output_in_thread(self):
@mx.compile
def fun(x):
Expand Down Expand Up @@ -1309,14 +1315,13 @@ def f(x):

def test_double_constant(self):
with mx.stream(mx.cpu):
x = mx.array(1.0, dtype=mx.float64)
x = mx.array([1.0], dtype=mx.float64)
constant = math.nextafter(1.0, 2.0)

def fun(x):
return (x + math.pi) * 2.0
return (x * x) * constant

y = fun(x).item()
y_compiled = mx.compile(fun)(x).item()
self.assertEqual(y, y_compiled)
self.assertTrue(mx.array_equal(fun(x), mx.compile(fun)(x)))

def test_shared_broadcast(self):
def fun(x, y, z):
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