Use std::countl_zero and std::countr_zero

vespalib/src/vespa/vespalib/util/optimized.h

@@ -2,26 +2,23 @@
 
 #pragma once
 
-#include <cstdint>
+#include <bit>
 
 namespace vespalib {
 
 /**
  * @brief Optimized instructions class
- *
- * Here are fast handcoded assembly functions for doing some special
- * low level functions that can be carried out very fast by special instructions.
- * Currently only implemented for GCC on i386 and x86_64 platforms.
  **/
 class Optimized
 {
 public:
-    static int msbIdx(unsigned int v) noexcept;
-    static int msbIdx(unsigned long v) noexcept;
-    static int msbIdx(unsigned long long v) noexcept;
-    static int lsbIdx(unsigned int v) noexcept;
-    static int lsbIdx(unsigned long v) noexcept;
-    static int lsbIdx(unsigned long long v) noexcept;
+
+    static constexpr int msbIdx(unsigned int v) noexcept { return v ? sizeof(unsigned int) * 8 - 1 - std::countl_zero(v) : 0; }
+    static constexpr int msbIdx(unsigned long v) noexcept { return v ? sizeof(unsigned long) * 8 - 1 - std::countl_zero(v) : 0; }
+    static constexpr int msbIdx(unsigned long long v) noexcept  { return v ? sizeof(unsigned long long) * 8 - 1 - std::countl_zero(v) : 0; }
+    static constexpr int lsbIdx(unsigned int v) noexcept { return v ? std::countr_zero(v) : 0; }
+    static constexpr int lsbIdx(unsigned long v) noexcept { return v ? std::countr_zero(v) : 0; }
+    static constexpr int lsbIdx(unsigned long long v) noexcept { return v ? std::countr_zero(v) : 0; }
 };
 
 /**
@@ -60,46 +57,6 @@ class Optimized
  * @return index [0-63] of lsb, 0 if none.
  **/
 
-#ifdef __x86_64__
-inline int Optimized::msbIdx(unsigned int v) noexcept {
-    unsigned int result;
-    __asm __volatile("bsrl %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-inline int Optimized::lsbIdx(unsigned int v) noexcept {
-    unsigned int result;
-    __asm __volatile("bsfl %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-inline int Optimized::msbIdx(unsigned long v) noexcept {
-    unsigned long result;
-    __asm __volatile("bsrq %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-inline int Optimized::lsbIdx(unsigned long v) noexcept {
-    unsigned long result;
-    __asm __volatile("bsfq %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-inline int Optimized::msbIdx(unsigned long long v) noexcept {
-    unsigned long long result;
-    __asm __volatile("bsrq %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-inline int Optimized::lsbIdx(unsigned long long v) noexcept {
-    unsigned long long result;
-    __asm __volatile("bsfq %0,%0" : "=r" (result) : "0" (v));
-    return result;
-}
-#else
-inline int Optimized::msbIdx(unsigned int v) noexcept { return v ? sizeof(unsigned int) * 8 - 1 - __builtin_clz(v) : 0; }
-inline int Optimized::msbIdx(unsigned long v) noexcept { return v ? sizeof(unsigned long) * 8 - 1 - __builtin_clzl(v) : 0; }
-inline int Optimized::msbIdx(unsigned long long v) noexcept  { return v ? sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(v) : 0; }
-inline int Optimized::lsbIdx(unsigned int v) noexcept { return v ? __builtin_ctz(v) : 0; }
-inline int Optimized::lsbIdx(unsigned long v) noexcept { return v ? __builtin_ctzl(v) : 0; }
-inline int Optimized::lsbIdx(unsigned long long v) noexcept { return v ? __builtin_ctzll(v) : 0; }
-#endif
-
 #define VESPA_DLL_LOCAL  __attribute__ ((visibility("hidden")))
 
 }