Intel ARCHITECTURE IA-32 User Manual download pdf (Page 308)

100

101

7-40 Vol. 3A

MULTIPLE-PROCESSOR MANAGEMENT

store returned value of eax

return (unsigned ) ((reg_eax >> 26) +1);

}

else // must be a single-core processor

return 1;

}

4. Extract the initial APIC ID of a logical processor.

#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;

}

5. Find the width of a bit-field mask from the maximum count of the bit-field.

// 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

mov eax, mask_width

}

return mask_width;

}

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Intel ARCHITECTURE IA-32 User Manual Page 308

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