Subversion Repositories zipcpu

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;
; Filename:     mpyu.S
;
; Project:      Zip CPU -- a small, lightweight, RISC CPU soft core
;
; Purpose:      Zip assembly file for running doing an unsigned 32x32 bit
;               multiply..
;
; Creator:      Dan Gisselquist, Ph.D.
;               Gisselquist Technology, LLC
;
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;
; Copyright (C) 2015, Gisselquist Technology, LLC
;
; This program is free software (firmware): you can redistribute it and/or
; modify it under the terms of  the GNU General Public License as published
; by the Free Software Foundation, either version 3 of the License, or (at
; your option) any later version.
;
; This program is distributed in the hope that it will be useful, but WITHOUT
; ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or
; FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
; for more details.
;
; License:      GPL, v3, as defined and found on www.gnu.org,
;               http://www.gnu.org/licenses/gpl.html
;
;
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;
;
mpy32u: ; unsigned R0 * unsigned R1 -> unsigned R0:R1, R2 = rtn addr (on stack)
        SUB     3,SP
        STO     R2,(SP)
        STO     R3,1(SP)
        STO     R4,2(SP)
        ;
        MOV     R0,R2
        MPYU    R1,R2   ; R2 = Low order bits, low(R0) * low(R1)
        MOV     R0,R3
        LSR     16,R3   ; Put high order bits in lower half of R3
        MPYU    R1,R3   ; R3 = Mid order bits, high(R0) * low(R1)
        LSR     16,R1   ; R1 = High order bits of R1, being done w/ low order
        MOV     R1,R4   ; 
        MPYU    R0,R4   ; R4 = Mid order bits, low(R0) * high(R1)
        LSR     16,R0
        MPYU    R1,R0   ; R0 = High order bits, high(R0) * high(R1)
        ADD     R3,R4   ; R4 = sum of mid order bits
        ADD.C   0x010000,R0     ; Add in the carry (if it happened)
        MOV     R4,R3   
        LSR     16,R3
        ADD     R3,R0   ; R0 = high order bits plus high order mid-bits 
        LSL     16,R4
        ADD     R4,R2   ; R2 = low order bits plus low order mid-bits
        ADD.C   1,R0    ; Add in the carry to R0 (if it happened)
        MOV     R2,R1   ; Place low order bits into R1
        ;
        LOD     (SP),R2
        LOD     1(SP),R3
        LOD     2(SP),R4
        ADD     3,SP
        JMP     R2