PIC18F44J50-I Datasheet, PDF (114/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

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Example 8-3 provides the instruction sequence for a
16 x 16 unsigned multiplication. Equation 8-1 provides
the algorithm that is used. The 32-bit result is stored in
four registers (RES<3:0>).
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 UNSIGNED
MULTIPLY ROUTINE
MOVF ARG1L, W
MULWF ARG2L
MOVFF PRODH, RES1
MOVFF PRODL, RES0
; ARG1L * ARG2L->
; PRODH:PRODL
;
;
MOVF ARG1H, W
MULWF ARG2H
MOVFF PRODH, RES3
MOVFF PRODL, RES2
; ARG1H * ARG2H->
; PRODH:PRODL
;
;
MOVF ARG1L, W
MULWF ARG2H
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG
RES3, F
; ARG1L * ARG2H->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
MOVF ARG1H, W
MULWF ARG2L
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG
RES3, F
;
; ARG1H * ARG2L->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
Example 8-4 provides the sequence to do a 16 x 16
signed multiply. Equation 8-2 provides the algorithm
used. The 32-bit result is stored in four registers
(RES<3:0>). To account for the sign bits of the
arguments, the MSb for each argument pair is tested
and the appropriate subtractions are done.
EQUATION 8-2: 16 x 16 SIGNED
MULTIPLICATION
ALGORITHM
RES3:RES0
= ARG1H:ARG1L · ARG2H:ARG2L
= (ARG1H · ARG2H · 2¹⁶) +
(ARG1H · ARG2L · 2⁸) +
(ARG1L · ARG2H · 2⁸) +
(ARG1L · ARG2L) +
(-1 · ARG2H<7> · ARG1H:ARG1L · 2¹⁶) +
(-1 · ARG1H<7> · ARG2H:ARG2L · 2¹⁶)
EXAMPLE 8-4:
16 x 16 SIGNED MULTIPLY
ROUTINE
MOVF ARG1L, W
MULWF ARG2L
MOVFF PRODH, RES1
MOVFF PRODL, RES0
; ARG1L * ARG2L ->
; PRODH:PRODL
;
;
MOVF ARG1H, W
MULWF ARG2H
MOVFF PRODH, RES3
MOVFF PRODL, RES2
; ARG1H * ARG2H ->
; PRODH:PRODL
;
;
MOVF ARG1L, W
MULWF ARG2H
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG
RES3, F
; ARG1L * ARG2H ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
MOVF ARG1H, W
MULWF ARG2L
MOVF
ADDWF
MOVF
ADDWFC
CLRF
ADDWFC
PRODL, W
RES1, F
PRODH, W
RES2, F
WREG
RES3, F
;
; ARG1H * ARG2L ->
; PRODH:PRODL
;
; Add cross
; products
;
;
;
BTFSS
BRA
MOVF
SUBWF
MOVF
SUBWFB
ARG2H, 7
SIGN_ARG1
ARG1L, W
RES2
ARG1H, W
RES3
; ARG2H:ARG2L neg?
; no, check ARG1
;
;
;
SIGN_ARG1
BTFSS
BRA
MOVF
SUBWF
MOVF
SUBWFB
ARG1H, 7
CONT_CODE
ARG2L, W
RES2
ARG2H, W
RES3
; ARG1H:ARG1L neg?
; no, done
;
;
;
CONT_CODE
:
DS39931D-page 114
 2011 Microchip Technology Inc.