truncate float in DType.const [pr] (#17439)

test/backend/test_dtype_alu.py

@@ -399,9 +399,10 @@ class TestDTypeALU(unittest.TestCase):
     if float_dtype not in supported_dtypes: float_dtype = dtypes.float32
     universal_test_cast(a, float_dtype, unsigned_dtype)
 
-  @unittest.expectedFailure
-  def test_unsafe_cast_float_to_int_failure(self):
-    val = float(dtypes.int32.max - 1)
+  def test_unsafe_cast_float_to_int(self):
+    # the value is off the float32 grid but rounds in-range: the buffer and const-fold paths must agree
+    # (out-of-range float->int cast stays undefined: hardware may saturate where the fold wraps)
+    val = 2147483000.0
     t1 = Tensor([val], dtype=dtypes.float32).cast(dtypes.int32)
     t2 = Tensor(val, dtype=dtypes.float32).cast(dtypes.int32)
     np.testing.assert_equal(t1.item(), t2.item())

test/null/test_const_folding.py

@@ -1,6 +1,6 @@
 import unittest, itertools, math
 from tinygrad import Tensor, dtypes, Context
-from tinygrad.dtype import DType, ConstType
+from tinygrad.dtype import DType, ConstType, truncate
 from tinygrad.uop.ops import Ops, UOp
 from test.helpers import full_rewrite
 import numpy as np
@@ -51,6 +51,17 @@ class TestWeakConstFolding(unittest.TestCase):
   def test_invalid_poison(self):
     self.assertTrue(UOp.invalid().alu(Ops.CDIV, UOp.const(0)).simplify().is_invalid)
 
+  def test_cast_commits_to_dtype_grid(self):
+    # committing a weak const to a stated width puts the value on that width's grid, same as storage packing and native compilers
+    v = 1/123008  # not representable in float16
+    out = UOp.const(v).cast(dtypes.half).simplify()
+    self.assertEqual((out.op, out.dtype, out.val), (Ops.CONST, dtypes.half, truncate[dtypes.half](v)))
+    self.assertNotEqual(out.val, v)
+    # the grid commit preserves the sign of zero
+    self.assertEqual(math.copysign(1, UOp.const(-0.0).cast(dtypes.half).simplify().val), -1)
+    # observable at tensor level: the const-folded comparison agrees with the committed value
+    self.assertTrue((Tensor(-3.2).cast(dtypes.float32) <= truncate[dtypes.float32](-3.2)).item())
+
 class TestBinaryOpsConstFolding(unittest.TestCase):
   def test_add_literal_zero(self):
     _check_ast_count(0, Tensor([1.0, 2, 3, 4]) + 0)

test/null/test_uop_vmin_vmax.py

@@ -1,6 +1,6 @@
 import unittest, math
 from tinygrad.uop.ops import UOp, Ops
-from tinygrad.dtype import dtypes, Invalid
+from tinygrad.dtype import dtypes, Invalid, truncate
 
 class TestVminVmaxProperties(unittest.TestCase):
   def test_vmin_vmax_constant(self):
@@ -317,8 +317,8 @@ class TestVminVmaxVConst(unittest.TestCase):
   def test_vmin_vmax_vconst_with_floats(self):
     # vmin and vmax for a vector constant of float values
     uop = UOp.const((1.5, -3.2, 0.0))
-    self.assertEqual(uop.vmin, -3.2)
-    self.assertEqual(uop.vmax, 1.5)
+    self.assertEqual(uop.vmin, truncate[dtypes.default_float](-3.2))
+    self.assertEqual(uop.vmax, truncate[dtypes.default_float](1.5))
 
   def test_vmin_vmax_vconst_with_bools(self):
     # vmin and vmax for a vector constant of bool values

tinygrad/dtype.py

@@ -80,7 +80,7 @@ class DType(metaclass=DTypeMetaClass):
     # NOTE: float('nan') != float('nan'), so we canonicalize here
     if isinstance(val, float) and math.isnan(val): val = math.nan
     # int is the default. wrap floats in ConstFloat to distinguish -0.0 from 0.0 in cache
-    return ConstFloat(float(val)) if dtypes.is_float(self) else bool(val) if dtypes.is_bool(self) else int(val)
+    return ConstFloat(truncate.get(self, float)(float(val))) if dtypes.is_float(self) else bool(val) if dtypes.is_bool(self) else int(val)
 
 
 class DTypes: