Microchip Technology MA160014 Data Sheet
PIC18(L)F2X/4XK22
DS41412F-page 112
2010-2012 Microchip Technology Inc.
shows the sequence to do a 16 x 16
unsigned multiplication.
shows the
algorithm that is used. The 32-bit result is stored in four
registers (RES<3:0>).
registers (RES<3:0>).
EQUATION 8-1:
16 x 16 UNSIGNED
MULTIPLICATION
ALGORITHM
MULTIPLICATION
ALGORITHM
EXAMPLE 8-3:
16 x 16 UNSIGNED
MULTIPLY ROUTINE
MULTIPLY ROUTINE
shows the sequence to do a 16 x 16
signed multiply.
shows the algorithm
used. The 32-bit result is stored in four registers
(RES<3:0>). To account for the sign bits of the argu-
ments, the MSb for each argument pair is tested and
the appropriate subtractions are done.
(RES<3:0>). To account for the sign bits of the argu-
ments, the MSb for each argument pair is tested and
the appropriate subtractions are done.
EQUATION 8-2:
16 x 16 SIGNED
MULTIPLICATION
ALGORITHM
MULTIPLICATION
ALGORITHM
EXAMPLE 8-4:
16 x 16 SIGNED
MULTIPLY ROUTINE
MULTIPLY ROUTINE
RES3:RES0
=
ARG1H:ARG1L
ARG2H:ARG2L
=
(ARG1H
ARG2H 2
16
) +
(ARG1H
ARG2L 2
8
) +
(ARG1L
ARG2H 2
8
) +
(ARG1L
ARG2L)
MOVF
ARG1L, W
MULWF
ARG2L
; ARG1L * ARG2L->
; PRODH:PRODL
MOVFF
PRODH, RES1
;
MOVFF
PRODL, RES0
;
;
MOVF
ARG1H, W
MULWF
ARG2H
; ARG1H * ARG2H->
; PRODH:PRODL
MOVFF
PRODH, RES3
;
MOVFF
PRODL, RES2
;
;
MOVF
ARG1L, W
MULWF
ARG2H
; ARG1L * ARG2H->
; PRODH:PRODL
MOVF
PRODL, W
;
ADDWF
RES1, F
; Add cross
MOVF
PRODH, W
; products
ADDWFC
RES2, F
;
CLRF
WREG
;
ADDWFC
RES3, F
;
;
MOVF
ARG1H, W
;
MULWF
ARG2L
; ARG1H * ARG2L->
; PRODH:PRODL
MOVF
PRODL, W
;
ADDWF
RES1, F
; Add cross
MOVF
PRODH, W
; products
ADDWFC
RES2, F
;
CLRF
WREG
;
ADDWFC
RES3, F
;
RES3:RES0 = ARG1H:ARG1L
ARG2H:ARG2L
= (ARG1H
ARG2H 2
16
) +
(ARG1H
ARG2L 2
8
) +
(ARG1L
ARG2H 2
8
) +
(ARG1L
ARG2L) +
(-1
ARG2H<7> ARG1H:ARG1L 2
16
) +
(-1
ARG1H<7> ARG2H:ARG2L 2
16
)
MOVF
ARG1L, W
MULWF
ARG2L
; ARG1L * ARG2L ->
; PRODH:PRODL
MOVFF
PRODH, RES1
;
MOVFF
PRODL, RES0
;
;
MOVF
ARG1H, W
MULWF
ARG2H
; ARG1H * ARG2H ->
; PRODH:PRODL
MOVFF
PRODH, RES3
;
MOVFF
PRODL, RES2
;
;
MOVF
ARG1L, W
MULWF
ARG2H
; ARG1L * ARG2H ->
; PRODH:PRODL
MOVF
PRODL, W
;
ADDWF
RES1, F
; Add cross
MOVF
PRODH, W
; products
ADDWFC
RES2, F
;
CLRF
WREG
;
ADDWFC
RES3, F
;
;
MOVF
ARG1H, W
;
MULWF
ARG2L
; ARG1H * ARG2L ->
; PRODH:PRODL
MOVF
PRODL, W
;
ADDWF
RES1, F
; Add cross
MOVF
PRODH, W
; products
ADDWFC RES2, F
;
CLRF
WREG
;
ADDWFC
RES3, F
;
;
BTFSS
ARG2H, 7
; ARG2H:ARG2L neg?
BRA
SIGN_ARG1
; no, check ARG1
MOVF
ARG1L, W
;
SUBWF
RES2
;
MOVF
ARG1H, W
;
SUBWFB
RES3
;
SIGN_ARG1
BTFSS
ARG1H, 7
; ARG1H:ARG1L neg?
BRA
CONT_CODE
; no, done
MOVF
ARG2L, W
;
SUBWF
RES2
;
MOVF
ARG2H, W
;
SUBWFB
RES3
;
CONT_CODE
: