getdata.s

实现了一个简单的快速傅立叶变化功能函数,对一副图象进行傅立叶变化,其中关键的变换部分是用汇编实现的

    AREA getData,CODE,READONLY
N	equ		128
	import	sin
	import	cos
	export	getsin
	export	getcos
common		;R0=c,R1=f
	mov		R2, #0
	mov 	R3,	#1
	mov		R4,	#N
	mov		R4,	R4,	lsr #1
	cmp		R3,	R0
	bge		commonend
loop
	add		R2,	R2,	R4
	mov		R4,	R4,	lsr #1
	add		R3,	R3,	#1
	cmp		R3,	R0
	blt		loop
commonend
	mov		PC,	LR
	
getsin
	stmfd	SP!,{LR}
	mov		LR,	PC
	b		common
	mov		R2,	R2,	lsl #2
	add		R2,	R2,	R1,	lsl #2
	ldr		R1,	=sin
	ldr		R12,	[R1,R2]			;R0返回sin值
	ldmfd	SP!,{LR}
	mov		PC,	LR
	

getcos
	stmfd	SP!,{LR}
	mov		LR,	PC
	bl		common
	mov		R2,	R2,	lsl #2
	add		R2,	R2,	R1,	lsl #2
	ldr		R1,	=cos
	ldr		R12,	[R1,R2]			;R0返回cos值
	ldmfd	SP!,{LR}
	mov		PC,	LR
	END