[Mlir-commits] [mlir] a383a48 - [mlir][tosa] Update the limit of 62 on shift.

[Eric Kunze]

Author: Peng Sun
Date: 2023-05-24T15:35:50-07:00
New Revision: a383a481eed123f91a0b8460c88122a7dbcbaaa1

URL: https://github.com/llvm/llvm-project/commit/a383a481eed123f91a0b8460c88122a7dbcbaaa1
DIFF: https://github.com/llvm/llvm-project/commit/a383a481eed123f91a0b8460c88122a7dbcbaaa1.diff

LOG: [mlir][tosa] Update the limit of 62 on shift.

  Aligns the shift requirement with the TOSA specification.

Reviewed By: eric-k256

Differential Revision: https://reviews.llvm.org/D151113

Added: 
    

Modified: 
    mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp

Removed: 
    


################################################################################
diff  --git a/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp b/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
index 1c4ae1f27319f..a164135aa0649 100644
--- a/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
+++ b/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
@@ -44,11 +44,13 @@ static void computeMultiplierAndShiftTosaScale16(double scale,
 
   multiplier = static_cast<int32_t>(shiftedM);
 
-  // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
-  if (shift > 63) {
+  // Shifting tops out at 62 bits. Right shift to make 62 bits the max.
+  // The limit of 62 on shift allows the shift to be decomposed as
+  // two right shifts of 31.
+  if (shift > 62) {
     // Shifting the multiplier by more than 31-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
-    shift = 63;
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 62);
+    shift = 62;
   }
 }
 
@@ -79,11 +81,13 @@ static void computeMultiplierAndShiftTosaScale32(double scale,
 
   multiplier = static_cast<int32_t>(shiftedM);
 
-  // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
-  if (shift > 63) {
+  // Shifting tops out at 62 bits. Right shift to make 62 bits the max.
+  // The limit of 62 on shift allows the shift to be decomposed as
+  // two right shifts of 31.
+  if (shift > 62) {
     // Shifting the multiplier by more than 32-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
-    shift = 63;
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 62);
+    shift = 62;
   }
 }