[arm][arm64] Improve CountTrailingZero implementation.

src/base/bits.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_BASE_BITS_H_
 #define V8_BASE_BITS_H_
 
 #include <stdint.h>
 #include "src/base/macros.h"
 #if V8_CC_MSVC
@@ skipping 74 matching lines @@
   value = value | (value >> 2);
   value = value | (value >> 4);
   value = value | (value >> 8);
   value = value | (value >> 16);
   value = value | (value >> 32);
   return CountPopulation64(~value);
 #endif
 }
 
 
+// ReverseBits(value) returns |value| in reverse bit order.
+template <typename T>
+T ReverseBits(T value) {
+  DCHECK((sizeof(value) == 1) || (sizeof(value) == 2) || (sizeof(value) == 4) ||
+         (sizeof(value) == 8));
+  T result = 0;
+  for (unsigned i = 0; i < (sizeof(value) * 8); i++) {
+    result = (result << 1) | (value & 1);
+    value >>= 1;
+  }
+  return result;
+}
+
+
 // CountTrailingZeros32(value) returns the number of zero bits preceding the
 // least significant 1 bit in |value| if |value| is non-zero, otherwise it
 // returns 32.
 inline unsigned CountTrailingZeros32(uint32_t value) {
 #if V8_HAS_BUILTIN_CTZ
   return value ? __builtin_ctz(value) : 32;
 #elif V8_CC_MSVC
   unsigned long result;  // NOLINT(runtime/int)
   if (!_BitScanForward(&result, value)) return 32;
   return static_cast<unsigned>(result);
@@ skipping 175 matching lines @@
 // truncated to uint32. If |rhs| is zero, then zero is returned.
 inline uint32_t UnsignedMod32(uint32_t lhs, uint32_t rhs) {
   return rhs ? lhs % rhs : 0u;
 }
 
 }  // namespace bits
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_BITS_H_