PIC17C75X
Example 9-3 shows the sequence to do a 16 x 16
unsigned multiply. Equation 9-1 shows the algorithm
that is used. The 32-bit result is stored in 4 registers
RES3:RES0.
EXAMPLE 9-3: 16 x 16 UNSIGNED
MULTIPLY ROUTINE
MOVFP
MULWF
ARG1L, WREG
ARG2L
; ARG1L * ARG2L ->
PRODH:PRODL
;
EQUATION 9-1:
16 x 16 UNSIGNED
MULTIPLICATION
ALGORITHM
MOVPF
MOVPF
PRODH, RES1 ;
PRODL, RES0 ;
;
;
MOVFP
MULWF
ARG1H, WREG
ARG2H
RES3:RES0
=
=
ARG1H:ARG1L • ARG2H:ARG2L
; ARG1H * ARG2H ->
PRODH:PRODL
16
;
(ARG1H • ARG2H • 2 )
+
+
+
MOVPF
MOVPF
PRODH, RES3 ;
PRODL, RES2 ;
8
(ARG1H • ARG2L • 2 )
8
(ARG1L • ARG2H • 2 )
MOVFP
MULWF
ARG1L, WREG
ARG2H
(ARG1L • ARG2L)
; ARG1L * ARG2H ->
;
PRODH:PRODL
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
PRODL, WREG ;
RES1, F
; Add cross
PRODH, WREG ;
products
RES2, F
WREG, F
RES3, F
;
;
;
ADDWFC
;
MOVFP
MULWF
ARG1H, WREG ;
ARG2L ; ARG1H * ARG2L ->
;
PRODH:PRODL
MOVFP
ADDWF
MOVFP
ADDWFC
CLRF
PRODL, WREG ;
RES1, F
; Add cross
PRODH, WREG ;
products
RES2, F
WREG, F
RES3, F
;
;
;
ADDWFC
DS30264A-page 62
Preliminary
1997 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
