Arm backend: Fix mult and scale calculation for int48_t

Signed-off-by: Per Åstrand <[email protected]>
Change-Id: Ibe158d8d35a632547290f1b9a055d061ae267d77

Author: per

backends/arm/tosa/quant_utils.py

@@ -262,6 +262,9 @@ def compute_multiplier_and_shift(
         if shift > 62:
             multiplier = multiplier >> min(31, shift - 62)
             shift = 62
+
+        assert multiplier >= 0, "Multiplier should be non-negative"
+        assert shift >= 2 and shift <= 62, "Shift should be in range [2, 62]"
         multipliers.append(multiplier)
         shifts.append(shift)
     return multipliers, shifts
@@ -315,8 +318,8 @@ def build_rescale(
     import serializer.tosa_serializer as ts  # type: ignore
     import tosa.Op as TosaOp  # type: ignore
 
-    scaleWidth = 32
-    is_scale32 = True
+    scaleWidth = 16 if input_node.dtype == ts.DType.INT48 else 32
+    is_scale32 = False if input_node.dtype == ts.DType.INT48 else True
     multipliers, shifts = compute_multiplier_and_shift(scale, scaleWidth)
     rescale_inputs = create_const_ops_for_rescale(
         tosa_fb,