
PIC17C4X
DS30412C-page 50
1996 Microchip Technology Inc.
that is used. The 32-bit result is stored in 4 registers
RES3:RES0.
EQUATION 8-1:
16 x 16 UNSIGNED
MULTIPLICATION
ALGORITHM
RES3:RES0
=
ARG1H:ARG1L * ARG2H:ARG2L
=
(ARG1H * ARG2H * 216)+
(ARG1H * ARG2L * 28)+
(ARG1L * ARG2H * 28)+
(ARG1L * ARG2L)
EXAMPLE 8-3:
16 x 16 MULTIPLY ROUTINE
MOVFP
ARG1L, WREG
MULWF
ARG2L
; ARG1L * ARG2L ->
;
PRODH:PRODL
MOVPF
PRODH, RES1 ;
MOVPF
PRODL, RES0 ;
;
MOVFP
ARG1H, WREG
MULWF
ARG2H
; ARG1H * ARG2H ->
;
PRODH:PRODL
MOVPF
PRODH, RES3 ;
MOVPF
PRODL, RES2 ;
;
MOVFP
ARG1L, WREG
MULWF
ARG2H
; ARG1L * ARG2H ->
;
PRODH:PRODL
MOVFP
PRODL, WREG ;
ADDWF
RES1, F
; Add cross
MOVFP
PRODH, WREG ;
products
ADDWFC
RES2, F
;
CLRF
WREG, F
;
ADDWFC
RES3, F
;
MOVFP
ARG1H, WREG ;
MULWF
ARG2L
; ARG1H * ARG2L ->
;
PRODH:PRODL
MOVFP
PRODL, WREG ;
ADDWF
RES1, F
; Add cross
MOVFP
PRODH, WREG ;
products
ADDWFC
RES2, F
;
CLRF
WREG, F
;
ADDWFC
RES3, F
;