;Example 3 - 22. Split Function ASM Listing for the FFT of two N-Point Real Sequences for the TMS320C62x DSP
*================================================================
* TEXAS INSTRUMENTS, INC.
* Real FFT/IFFT split operation
*================================================================
.global _split
_split:
ldh .d2 *XPtr,X1r ; X1r = Xr[0]
ldh .d2 *+XPtr[1],X2r ; X2r = Xi[0]
sth .d1 X1r, *X1Ptr ; X1r[0]=Xr[0]
shl .s1 N, 2, N4 ; N4 = 4*N
|| sth .d2 X2r, *X2Ptr ; X2r[0]=Xi[0]
|| zero .l2 nullB ; nullA = 0
|| zero .l1 nullA ; nullB = 0
sub .l1 N4, 4, N4 ; N4 = N4 - 1
|| sth .d1 nullA, *+X1Ptr[1] ; X1i[0]=0
|| sth .d2 nullB, *+X2Ptr[1] ; X2i[0]=0
add .l1x N4, XPtr, XNmkPtr ; XNmkPtr -> X[N-1]
|| add .l2 XPtr, 4, XPtr ; XPTR -> X[1]
ldw .d2 *XPtr++[1], XiXr ; load X[k].re and X2[k].im
|| ldw .d1 *XNmkPtr--[1], XNiXNr ; load X[N-k].re and X[N-k].im
shr .s2x N, 1, CNT ; CNT = N/2
sub .s2 CNT, 1, CNT ; CNT = N/2 - 1
add .l1 N4, X1Ptr, X1NmkPtr ; X1NmkPtr -> X1[N-1]
|| add .l2x N4, X2Ptr, X2NmkPtr ; X2NmkPtr -> X2[N-1]
add .l X1Ptr, 4, X1Ptr ; X1Ptr -> X1[1]
|| add .l X2Ptr, 4, X2Ptr ; X2Ptr -> X2[1]
add2 .s1x XiXr, XNiXNr, X2rX1r ; X2[k].re = X[k].im + X[N-k].im
; (upper 16 bits)
; X1[k].re = X[k].re + X[N-k].re
; (lower 16 bits)
|| sub2 .s2x XiXr, XNiXNr, X1iX2i ; X1[k].im = X[k].im - X[N-k].im
; (upper 16 bits)
; X2[k].im = X[k].re - X[N-k].re
; (lower 16 bits)
|| ldw .d2 *XPtr++[1], XiXr ; load X[k].real and X2[k].imag
|| ldw .d1 *XNmkPtr--[1], XNiXNr ; load X[N-k].re and X[N-k].im
shr .s1 X2rX1r, 17, X2r ; X2[k].re=(X[k].im+X[N-k].im)/2
; X2r = X2rX1r>>17
|| sub2 .s2 nullB, X1iX2i, X2i ; X2[k].im=X[N-k].re-X[k].re
; (lower 16 bits)
; upper 16 bits are don't cares
shr .s2 X1iX2i, 17, X1i ; X1[k].im=(X[k].im+X[N-k].im)/2
; X1i = X1iX2i>>17
|| b .s1 LOOP ; branch for the first time through loop
LOOP:
ext .s1 X2rX1r, 16,17, X1r ; X1[k].real = X1[k].real/2
|| ext .s2 X2i, 16,17, X2i ; X2[k].imag = X2[k].imag/2
|| sth .d1 X1i, *+X1Ptr[1] ; store X1[k].imag
|| sth .d2 X2r, *X2Ptr++[1] ; store X2[k].real
mv .l1 X1r, X1Nr ; X1[N-k].real = X1[k].real
|| mv .s1 X2r, X2Nr ; X2[N-k].real = X2[k].real
|| sub .l2 nullB, X1i, X1Ni ; X1[N-k].imag = -X1[k].imag
|| sub .s2 nullB, X2i, X2Ni ; X2[N-k].imag = -X2[k].imag
|| sth .d2 X2i, *X2Ptr++[1] ; store X2[k].imag
|| sth .d1 X1r, *X1Ptr++[2] ; store X1[k].real
add2 .s1x XiXr, XNiXNr, X2rX1r ; X2[k].re = X[k].im + X[N-k].im
; (upper 16 bits)
; X1[k].re = X[k].re + X[N-k].re
; (lower 16 bits)
|| sub2 .s2x XiXr, XNiXNr, X1iX2i ; X1[k].im = X[k].im - X[N-k].im
; (upper 16 bits)
; X2[k].im = X[k].re - X[N-k].re
; (lower 16 bits)
|| ldw .d2 *XPtr++[1], XiXr ; load X[k].real and X2[k].imag
|| ldw .d1 *XNmkPtr--[1], XNiXNr ; load X[N-k].re and X[N-k].im
shr .s1 X2rX1r, 17, X2r ; X2[k].re=(X[k].im+X[N-k].im)/2
; X2r = X2rX1r>>17
|| sub2 .s2 nullB, X1iX2i, X2i ; X2[k].im=X[N-k].re-X[k].re
; (lower 16 bits)
; upper 16 bits are don't cares
|| sth .d1 X1Ni, *+X1NmkPtr[1] ; store X1[N-k].imag
|| sth .d2 X2Nr, *X2NmkPtr--[2] ; store X2[N-k].real
||[CNT] sub .l2 CNT, 1, CNT ; decrement loop counter
shr .s2 X1iX2i, 17, X1i ; X1[k].im=(X[k].im+X[N-k].im)/2
; X1i = X1iX2i>>17
|| sth .d1 X1Nr, *X1NmkPtr--[2] ; store X1[N-k].real
|| sth .d2 X2Ni, *+X2NmkPtr[3] ; store X2[N-k].imag
||[CNT] b .s1 LOOP ; LOOP END
nop 3 ; fill delay slots
