Intel architecture ia-32 User Manual

7-40 Vol. 3A

store returned value of eax
return (unsigned ) ((reg_eax >> 26) +1);

}
else // must be a single-core processor
return 1;

}

#define INITIAL_APIC_ID_BITS 0xFF000000 // EBX[31:24] initial APIC ID

// Returns the 8-bit unique initial APIC ID for the processor ruuning the code. 
// Software can use OS services to affinitize the current thread to each logical processor 
// available under the OS to gather the initial APIC_IDs for each logical processor.

unsigned char GetInitAPIC_ID (void)
{

unsigned int reg_ebx = 0;
execute cpuid with eax = 1
store returned value of ebx
return (unsigned char) ((reg_ebx & INITIAL_APIC_ID_BITS) >> 24;

}

// Returns the mask bit width of a bit field from the maximum count that bit field can represent.
// This algorithm does not assume ‘Max_Count’ to have a value equal to power of 2.

unsigned FindMaskWidth(Unsigned Max_Count)
{unsigned int mask_width, cnt = Max_Count;

__asm {

mov eax, cnt
mov ecx, 0
mov mask_width, ecx
dec eax
bsr cx, ax
jz next
inc cx
mov  mask_width, ecx
next:  
mov eax, mask_width

}

return mask_width;

}