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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <cstdint>
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);
static int msbIdx(unsigned long v);
static int msbIdx(unsigned long long v);
static int lsbIdx(unsigned int v);
static int lsbIdx(unsigned long v);
static int lsbIdx(unsigned long long v);
static constexpr int popCount(unsigned int v) { return __builtin_popcount(v); }
static constexpr int popCount(unsigned long v) { return __builtin_popcountl(v); }
static constexpr int popCount(unsigned long long v) { return __builtin_popcountll(v); }
};
/**
* @fn int Optimized::msbIdx(uint32_t v)
* @brief Quickly find most significant bit.
*
* Finds the position of the most significant '1'.
* @param v is the value to search
* @return index [0-31] of msb, 0 if none.
**/
/**
* @fn int Optimized::msbIdx(uint64_t v)
* @brief Quickly find most significant bit.
*
* Finds the position of the most significant '1'.
* @param v is the value to search
* @return index [0-63] of msb, 0 if none.
**/
/**
* @fn int Optimized::lsbIdx(uint32_t v)
* @brief Quickly find least significant bit.
*
* Finds the position of the least significant '1'.
* @param v is the value to search
* @return index [0-31] of lsb, 0 if none.
**/
/**
* @fn int Optimized::lsbIdx(uint64_t v)
* @brief Quickly find least significant bit.
*
* Finds the position of the least significant '1'.
* @param v is the value to search
* @return index [0-63] of lsb, 0 if none.
**/
#ifdef __x86_64__
inline int Optimized::msbIdx(unsigned int v) {
unsigned int result;
__asm __volatile("bsrl %0,%0" : "=r" (result) : "0" (v));
return result;
}
inline int Optimized::lsbIdx(unsigned int v) {
unsigned int result;
__asm __volatile("bsfl %0,%0" : "=r" (result) : "0" (v));
return result;
}
inline int Optimized::msbIdx(unsigned long v) {
unsigned long result;
__asm __volatile("bsrq %0,%0" : "=r" (result) : "0" (v));
return result;
}
inline int Optimized::lsbIdx(unsigned long v) {
unsigned long result;
__asm __volatile("bsfq %0,%0" : "=r" (result) : "0" (v));
return result;
}
inline int Optimized::msbIdx(unsigned long long v) {
unsigned long long result;
__asm __volatile("bsrq %0,%0" : "=r" (result) : "0" (v));
return result;
}
inline int Optimized::lsbIdx(unsigned long long v) {
unsigned long long result;
__asm __volatile("bsfq %0,%0" : "=r" (result) : "0" (v));
return result;
}
#else
inline int Optimized::msbIdx(unsigned int v) { return v ? sizeof(unsigned int) * 8 - 1 - __builtin_clz(v) : 0; }
inline int Optimized::msbIdx(unsigned long v) { return v ? sizeof(unsigned long) * 8 - 1 - __builtin_clzl(v) : 0; }
inline int Optimized::msbIdx(unsigned long long v) { return v ? sizeof(unsigned long long) * 8 - 1 - __builtin_clzll(v) : 0; }
inline int Optimized::lsbIdx(unsigned int v) { return v ? __builtin_ctz(v) : 0; }
inline int Optimized::lsbIdx(unsigned long v) { return v ? __builtin_ctzl(v) : 0; }
inline int Optimized::lsbIdx(unsigned long long v) { return v ? __builtin_ctzll(v) : 0; }
#endif
#define VESPA_DLL_LOCAL __attribute__ ((visibility("hidden")))
}
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