example 2-15.sa

《基于TI DSP的通用算法实现》程序代码

;Example 2 - 15. Double-Precision Floating-Point Square Root SA Listing for sqrt

;================================================================
; Copyright 1998 by Texas Instruments Inc. All rights reserved.
; SQRDP.sa Syd Poland 06-24-98 for TMS320C67xx DSPs
; a5:a4 = a5:a4
; ans = Square Root (arg1) DP FP Square Root Subroutine
;================================================================

	.text			; program memory
	.global _SQRDP, _sqrt	; entry labels
	.align	32		; fetch packet boundary

_sqrt					; entry in rts6701 library
_SQRDP .cproc arg1H:arg1L		; entry to DP FP square root function
					; declare the input arguments

	.reg VH:VL, ansH:ansL, xH:xL, KH:KL, tH:tL, exp1
			
	clr	arg1H, 31, 31, arg1H	; force sign bit to +
	zero	VH			; V = 0

	extu	arg1H, 1, 21, exp1		; exp1 = 0 ?
	rsqrdp	arg1H:arg1L, xH:xL		; x1 = TLU (1/arg1) [8-bits]
	extu	arg1H, 1, 21, exp1		; get exponent 1 field
  [exp1]set	VH,20,20,VH				; V = 1 in exponent field
	sub	arg1H,VH,VH				; V = arg1 / 2 if exp1 > 0

	mv	arg1L,VL
	mpydp	VH:VL, xH:xL, tH:tL		; t = (arg1/2) * x1

	zero	KH ; K = 0
	zero	KL
	set	KH,19,29,KH			; 1.5 in DP FP (0x3ff8_0000)
	mpydp	xH:xL, tH:tL, tH:tL		; t = [(arg1/2)*x1] * x1
	subdp	KH:KL, tH:tL, tH:tL		; t = 1.5-[(arg1/2)*x1]*x1

	mpydp	xH:xL, tH:tL, xH:xL 		; x2=x1*{1.5-(arg1/2)*(x1*x1)}
	mpydp	VH:VL, xH:xL, tH:tL		; t = (arg1/2) * x2
	mpydp	xH:xL, tH:tL, tH:tL		; t = [(arg1/2)*x2] * x2
	subdp	KH:KL, tH:tL, tH:tL		; t = 1.5-[(arg1/2)*x2]*x2

	mpydp	xH:xL, tH:tL, xH:xL		; x3=x2*{1.5-(arg1/2)*(x2*x2)}
	mpydp	VH:VL, xH:xL, tH:tL		; t = (arg1/2) * x3
	mpydp	xH:xL, tH:tL, tH:tL		; t = [(arg1/2)*x3] * x3

	subdp	KH:KL, tH:tL, tH:tL		; t = 1.5-[(arg1/2)*x3]*x3
	mpydp	xH:xL, tH:tL, xH:xL		; x4=x3*{1.5-(arg1/2)*(x3*x3)}
  [exp1]mpydp	arg1H:arg1L, xH:xL, ansH:ansL	; ans=arg1*x3 (exp1>0)
 [!exp1]zero	ansH				; ans = 0 if exp1 = 0
 [!exp1	zeroansL

	.return ansH:ansL
	.endproc