exp4c54_7.asm

用dsp解压mp3程序的算法

**************************************************************
* exp4c54_7.asm - An assembly program for C5000 CCS simulator
*               Special case of multiplication in Section 4.6.7
*     
**************************************************************
* Section allocation
*
	.def	 x,yh,y,init
x       .usect   "vars",2    ; reserve 2 locations for x
y	.usect   "vars",1    ; reserve 1 location for y
yh	.usect   "vars",1    ; reserve 1 location for yh

	.sect "table"
init    .int -32768,-32768

	.text		     ; create code section
	.def	 start	     ; label of the beginning of code

start:
	NOP

copy:
    STM #x, AR1
    RPT #1
    MVPD init, *AR1+
	
mult:
	.mmregs
	SSBX FRCT
	SSBX SXM	; turn-on sign extension
	SSBX OVM	; turn-on Overflow mode
	;RSBX OVM	; turn-off Overflow mode (allow overflow)
	STM #x, AR1
	STM #(x+1),AR2
	LD *AR1, T
	MPY *AR2,A

	
* Write the result to memory location y

write:
	STL	A,*(y)	; y <- AL
	STH A,*(yh)	; yh <- AH
end
	NOP
	B	end	; stop here