fixes mask building in bit_sub

Minres · Feb 18, 2023 · cd08370 · cd08370
1 parent 9da215c
commit cd08370
Showing 1 changed file with 7 additions and 4 deletions.
diff --git a/src/common/util/ities.h b/src/common/util/ities.h
@@ -46,15 +46,18 @@
 template <unsigned int bit, unsigned int width, typename T>
 inline constexpr typename std::enable_if<std::is_unsigned<T>::value, T>::type bit_sub(T v) {
     static_assert((bit+width)<=8*sizeof(T));
-    return (v >> bit) & ((T(1) << width) - 1);
+    T res = (v >> bit) & ((T(1) << width) - 1);
+    return res;
 }
 
 template <unsigned int bit, unsigned int width, typename T>
 inline constexpr typename std::enable_if<std::is_signed<T>::value, T>::type bit_sub(T v) {
     static_assert((bit+width)<=8*sizeof(T));
-    auto sign = (1 << (bit + width - 1)) & v;
-    auto mask = ((T(1) << width) - 1);
-    return sign? (v >> bit) | mask : (v >> bit) & mask;
+    static_assert(width>0);
+    auto field = v>>bit;
+    auto amount = (field & ~(~T(1) << (width - 1) << 1)) -
+                  (field & (T(1) << (width - 1)) << 1);
+    return amount;
 }
 /**
  * @brief sign-extend a given value