exp4c54_3.asm

用dsp解压mp3程序的算法

*********************************************************************************
* exp4c54_3.asm - An assembly program for C5000 CCS simulator
*                 Overflow handling of y = Sum (xi) i = 1 to 8 in Section 4.6.3
*     
*********************************************************************************
* Section allocation
*
	.def	 x,y,init
x	.usect "vars",8	; reserve 8 locations for x
y	.usect "vars",1	; reserve 1 location for y

	.sect	 "table"
init	.int	 19660, 19660, 6554, -9830, -32768, -29491, 9830, 6554
						
			; adding these numbers : 0.6+0.6+0.2-0.3-1-0.9+0.3+0.2
	.text		; create code section
	.def	 start	; label of the beginning of code

* Copy data to vector x using indirect addressing mode

start:
	NOP
copy:	
	STM	#x,AR1	; AR0 pointing to x0
	RPT	#7      ; repeat next instruction 8 times
	MVPD init,*AR1+ ; copy 8 data to x
	

add:
	SSBX SXM	; turn on sign-extension mode
	;RSBX OVM	; turn on(SSBX)/off(RSBX) overflow mode
	SSBX OVM	; to view the different in the result...
	STM #x, AR2	; DP pointing to vector x0
	RPTZ A,#7	; A = 0, Set repeat counter to 8 counts
	ADD *AR2+,16, A ; shift numbers by 16 bits to left 
			; before adding them together			 

* Write the result to memory location y

write:
	STH	A,*(y)	; y <- A

end:
	NOP
	B	end