atom.h

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/***************************************************************************************************
 * Copyright 2025 NVIDIA Corporation. All rights reserved.
 **************************************************************************************************/
 
#ifndef MI_BASE_ATOM_H
#define MI_BASE_ATOM_H
 
#include <mi/base/config.h>
#include <mi/base/types.h>
 
// Select implementation to use.
#if !defined( MI_BASE_ATOM32_USE_ATOMIC) && !defined( MI_BASE_ATOM32_USE_ASSEMBLY)
#if defined( MI_ARCH_X86) && (defined( MI_COMPILER_GCC) || defined( MI_COMPILER_ICC))
#  define MI_BASE_ATOM32_USE_ASSEMBLY
#else
#  define MI_BASE_ATOM32_USE_ATOMIC
#endif
#endif
 
// Sanity check.
#if ! (defined( MI_BASE_ATOM32_USE_ATOMIC) ^ defined( MI_BASE_ATOM32_USE_ASSEMBLY))
#error Exactly one of MI_BASE_ATOM32_USE_ATOMIC and MI_BASE_ATOM32_USE_ASSEMBLY should be defined.
#endif
 
#if defined( MI_BASE_ATOM32_USE_ATOMIC)
#include <atomic>
#endif
 
namespace mi {
 
namespace base {
 
class Atom32
{
public:
    Atom32() : m_value( 0) { }
 
    Atom32( const Uint32 value) : m_value( value) { }
 
#ifndef MI_BASE_ATOM32_USE_ASSEMBLY
    Atom32( const Atom32& other);
 
    Atom32& operator=( const Atom32& rhs);
#endif
 
    Uint32 operator=( const Uint32 rhs) { m_value = rhs; return rhs; }
 
    Uint32 operator+=( const Uint32 rhs);
 
    Uint32 operator-=( const Uint32 rhs);
 
    Uint32 operator++();
 
    Uint32 operator++( int);
 
    Uint32 operator--();
 
    Uint32 operator--( int);
 
    operator Uint32() const { return m_value; }
 
    Uint32 swap( const Uint32 rhs);
 
private:
#ifdef MI_BASE_ATOM32_USE_ASSEMBLY
    // The counter.
    volatile Uint32 m_value;
#else
    // The counter.
    std::atomic_uint32_t m_value;
#endif
};
 
#ifndef MI_FOR_DOXYGEN_ONLY
 
#ifdef MI_BASE_ATOM32_USE_ASSEMBLY
 
inline Uint32 Atom32::operator+=( const Uint32 rhs)
{
    Uint32 retval;
    asm volatile(
        "movl %2,%0\n"
        "lock; xaddl %0,%1\n"
        "addl %2,%0\n"
        : "=&r"( retval), "+m"( m_value)
        : "r"( rhs)
        : "cc"
        );
    return retval;
}
 
inline Uint32 Atom32::operator-=( const Uint32 rhs)
{
    Uint32 retval;
    asm volatile(
        "neg %2\n"
        "movl %2,%0\n"
        "lock; xaddl %0,%1\n"
        "addl %2,%0\n"
        : "=&r"( retval), "+m"( m_value)
        : "r"( rhs)
        : "cc", "%2"
        );
    return retval;
}
 
inline Uint32 Atom32::operator++()
{
    Uint32 retval;
    asm volatile(
        "movl $1,%0\n"
        "lock; xaddl %0,%1\n"
        "addl $1,%0\n"
        : "=&r"( retval), "+m"( m_value)
        :
        : "cc"
        );
    return retval;
}
 
inline Uint32 Atom32::operator++( int)
{
    Uint32 retval;
    asm volatile(
        "movl $1,%0\n"
        "lock; xaddl %0,%1\n"
        : "=&r"( retval), "+m"( m_value)
        :
        : "cc"
        );
    return retval;
}
 
inline Uint32 Atom32::operator--()
{
    Uint32 retval;
    asm volatile(
        "movl $-1,%0\n"
        "lock; xaddl %0,%1\n"
        "addl $-1,%0\n"
        : "=&r"( retval), "+m"( m_value)
        :
        : "cc"
        );
    return retval;
}
 
inline Uint32 Atom32::operator--( int)
{
    Uint32 retval;
    asm volatile(
        "movl $-1,%0\n"
        "lock; xaddl %0,%1\n"
        : "=&r"( retval), "+m"( m_value)
        :
        : "cc"
        );
    return retval;
}
 
inline Uint32 Atom32::swap( const Uint32 rhs)
{
    Uint32 retval;
    asm volatile(
    "0:\n"
        "movl %1,%0\n"
        "lock; cmpxchg %2,%1\n"
        "jnz 0b\n"
        : "=&a"( retval), "+m"( m_value)
        : "r"( rhs)
        : "cc"
        );
    return retval;
}
 
#else
 
inline Atom32::Atom32( const Atom32& other) : m_value( other.m_value.load()) { }
 
inline Atom32& Atom32::operator=( const Atom32& rhs)
{
    m_value = rhs.m_value.load();
    return *this;
}
 
inline Uint32 Atom32::operator+=( const Uint32 rhs)
{
    m_value += rhs;
    return m_value;
}
 
inline Uint32 Atom32::operator-=( const Uint32 rhs)
{
    m_value -= rhs;
    return m_value;
}
 
inline Uint32 Atom32::operator++()
{
    return ++m_value;
}
 
inline Uint32 Atom32::operator++( int)
{
    return m_value++;
}
 
inline Uint32 Atom32::operator--()
{
    return --m_value;
}
 
inline Uint32 Atom32::operator--( int)
{
    return m_value--;
}
 
inline Uint32 Atom32::swap( const Uint32 rhs)
{
    return m_value.exchange( rhs);
}
 
#endif // MI_BASE_ATOM32_USE_ASSEMBLY
 
#endif // !MI_FOR_DOXYGEN_ONLY
 // end group mi_base_threads
 
} // namespace base
 
} // namespace mi
 
#endif // MI_BASE_ATOM_H