32-Bit Integer Multiplication
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; This routine multiplies two 32-bit signed integers
; resulting; in a 64-bit product. The operands are fetched
; from data memory and the result is written back to data
; memory.
; Data Storage:
; X1,X0 32-bit operand
; Y1,Y0 32-bit operand
; W3,W2,W1,W0 64-bit product
; Entry Conditions:
; SXM = 1, OVM = 0
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STM #X0,AR2   ;AR2 = X0 addr
STM #Y0,AR3   ;AR3 = Y0 addr
LD *AR2,T   ;T = X0
MPYU *AR3+,A   ;A = X0*Y0
STL A,@W0   ;save W0
LD A,–16,A   ;A = A >> 16
MACSU *AR2+,*AR3–,A  ;A = X0*Y0>>16 + X0*Y1
MACSU *AR3+,*AR2,A  ;A = X0*Y0>>16 + X0*Y1 + X1*Y0
STL A,@W1   ;save W1
LD A,–16,A   ;A = A >> 16
MAC *AR2,*AR3,A  ;A = (X0*Y1 + X1*Y0)>>16 + X1*Y1
STL A,@W2   ;save W2
STH A,@W3   ;save W3