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Chapter 8 Integer Optimizations 171
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
64-Bit Right Shift
shrd eax, edx, cl ; First apply shift count.
shr edx, cl ; mod 32 to EDX:EAX
test ecx, 32 ; Need to shift by another 32?
jz rshift_done ; No, done.
mov eax, edx ; Left shift EDX:EAX
xor edx, edx ; by 32 bits.
rshift_done:
64-Bit Multiplication
; _llmul computes the low-order half of the product of its
; arguments, two 64-bit integers.
;
; In: [ESP+8]:[ESP+4] = multiplicand
; [ESP+16]:[ESP+12] = multiplier
; Out: EDX:EAX = (multiplicand * multiplier) % 2^64
; Destroys: EAX, ECX, EDX, EFlags
_llmul PROC
mov edx, [esp+8] ; multiplicand_hi
mov ecx, [esp+16] ; multiplier_hi
or edx, ecx ; One operand >= 2^32?
mov edx, [esp+12] ; multiplier_lo
mov eax, [esp+4] ; multiplicand_lo
jnz twomul ; Yes, need two multiplies.
mul edx ; multiplicand_lo * multiplier_lo
ret ; Done, return to caller.
twomul:
imul edx, [esp+8] ; p3_lo = multiplicand_hi * multiplier_lo
imul ecx, eax ; p2_lo = multiplier_hi * multiplicand_lo
add ecx, edx ; p2_lo + p3_lo
mul dword ptr [esp+12] ; p1 = multiplicand_lo * multiplier_lo
add edx, ecx ; p1 + p2_lo + p3_lo = result in EDX:EAX
ret ; Done, return to caller.
_llmul ENDP
64-Bit Unsigned Division
; _ulldiv divides two unsigned 64-bit integers and returns the quotient.
;
; In: [ESP+8]:[ESP+4] = dividend
; [ESP+16]:[ESP+12] = divisor
; Out: EDX:EAX = quotient of division
; Destroys: EAX, ECX, EDX, EFlags
_ulldiv PROC
push ebx ; Save EBX as per calling convention.
mov ecx, [esp+20] ; divisor_hi
mov ebx, [esp+16] ; divisor_lo