Biegral Blog

        在x264中，x264_cpu_detect函数定义为：

uint32_t x264_cpu_detect( void )
{
    uint32_t cpu = 0;  // 定义CPU的型号，初始化为0

    uint32_t eax, ebx, ecx, edx;
    int      b_amd;


    if( !x264_cpu_cpuid_test() )
    {
        /* No cpuid */
        return 0;
    }

    x264_cpu_cpuid( 0, &eax, &ebx, &ecx, &edx);
    if( eax == 0 )
    {
        return 0;
    }
    b_amd   = (ebx == 0x68747541) && (ecx == 0x444d4163) && (edx == 0x69746e65);

    x264_cpu_cpuid( 1, &eax, &ebx, &ecx, &edx );
    if( (edx&0x00800000) == 0 )
    {
        /* No MMX */
        return 0;
    }
    cpu = X264_CPU_MMX;
    if( (edx&0x02000000) )
    {
        /* SSE - identical to AMD MMX extensions */
        cpu |= X264_CPU_MMXEXT|X264_CPU_SSE;
    }
    if( (edx&0x04000000) )
    {
        /* Is it OK ? */
        cpu |= X264_CPU_SSE2;
    }

    x264_cpu_cpuid( 0x80000000, &eax, &ebx, &ecx, &edx );
    if( eax < 0x80000001 )
    {
        /* no extended capabilities */
        return cpu;
    }

    x264_cpu_cpuid( 0x80000001, &eax, &ebx, &ecx, &edx );
    if( edx&0x80000000 )
    {
        cpu |= X264_CPU_3DNOW;
    }
    if( b_amd && (edx&0x00400000) )
    {
        /* AMD MMX extensions */
        cpu |= X264_CPU_MMXEXT;
    }

    return cpu;
}

      函数返回的是cpu的型号，本人在运行程序时，发现最后返回的cpu为15.

      接着看一下两个特殊的函数x264_cpu_cpuid_test和x264_cpu_cpuid，在程序中没有发现这两个函数的定义啊，那怎么能调用呢？原来，这两个函数是用汇编形式定义的：

x264_cpu_cpuid_test:
    pushfd
    push    ebx
    push    ebp
    push    esi
    push    edi

    pushfd
    pop     eax
    mov     ebx, eax
    xor     eax, 0x200000
    push    eax
    popfd
    pushfd
    pop     eax
    xor     eax, ebx
    
    pop     edi
    pop     esi
    pop     ebp
    pop     ebx
    popfd
    ret

x264_cpu_cpuid:

    push    ebp
    mov     ebp,    esp
    push    ebx
    push    esi
    push    edi
    
    mov     eax,    [ebp +  8]
    cpuid

    mov     esi,    [ebp + 12]
    mov     [esi],  eax

    mov     esi,    [ebp + 16]
    mov     [esi],  ebx

    mov     esi,    [ebp + 20]
    mov     [esi],  ecx

    mov     esi,    [ebp + 24]
    mov     [esi],  edx

    pop     edi
    pop     esi
    pop     ebx
    pop     ebp
    ret

       原来如此.