fix test_div_numerator_negative (#10229)

the simplification was wrong with negative const_factor

test/unit/test_uop_symbolic.py

@@ -351,9 +351,8 @@ class TestSymbolic(unittest.TestCase):
   def test_sum_div_partial_remove(self):
     self.helper_test_variable(usum([Variable("idx0", 0, 127)*4, Variable("idx2", 0, 3)])//4, 0, 127, "idx0")
 
-  # TODO: this is wrong
   def test_div_numerator_negative(self):
-    self.helper_test_variable((Variable("idx", 0, 9)*-10)//11, -9, 0, "(idx*-1)")
+    self.helper_test_variable((Variable("idx", 0, 9)*-10)//11, -8, 0, "(((idx*10)//11)*-1)")
 
   def test_div_into_mod(self):
     self.helper_test_variable((Variable("idx", 0, 16)*4)%8//4, 0, 1, "(idx%2)")

tinygrad/codegen/symbolic.py

@@ -152,7 +152,7 @@ def div_and_mod_folding(x: UOp, y: UOp, which: Literal[Ops.MOD, Ops.IDIV], split
   # a//c = (a-a%c)/c, if we can fold a%c, we can fold a//c
   # within a mod we can freely subtract multiples of c, we use this to see if a is congruent to an expression whose vmin/vmax are between 0 and c
   rems = [min(r, r-c, key=abs) for r in remainders]
-  if (rem:=sum(r*v for r,v in zip(rems,svars))+const%c).vmin//c==rem.vmax//c:
+  if (rem:=sum(r*v for r,v in zip(rems,svars))+const%c).vmin//c==rem.vmax//c and all(f > 0 for f in factors):
     if which is Ops.MOD: return rem - rem.vmin//c*c
     return sum((f-r)//c * v for f,r,v in zip(factors,rems,svars)) + (const-const%c+rem.vmin//c*c)//c
 

tinygrad/ops.py

@@ -598,6 +598,7 @@ class UOp(MathTrait, metaclass=UOpMetaClass):
     return False  # False if not sure
   def const_factor(self) -> int:
     """largest known int that divides self"""
+    # TODO: for negatives it's not the largest
     if self.op is Ops.CONST: return self.arg
     if self.op is Ops.VCONST: return math.gcd(*self.arg)
     if self.op is Ops.ADD: return math.gcd(self.src[0].const_factor(), self.src[1].const_factor())