?? example 3-20.asm
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;Example 3 - 20. Complex Bit Reversion Implementation ASM Listing for TMS320C62x
* ========================================================================= *
* TEXAS INSTRUMENTS, INC. *
* *
* NAME *
* DSP_bitrev_cplx *
* *
* REVISION DATE *
* 18-Sep-2001 *
* *
* USAGE *
* This routine is C Callable and can be called as: *
* *
* void DSP_bitrev_cplx(int *x, short *index, int nx) *
* *
* x[nx] : Input array to be bit-reversed. *
* index[]: Array of size ~sqrt(nx) created by the routine *
* bitrev_index to allow the fast implementation of the *
* bit-reversal. *
* nx : Number of points in array x[]. Must be power of 2. *
* *
* DESCRIPTION *
* This routine performs the bit-reversal of the input array x[]. *
* where x[] is an array of length nx 16-bit complex pairs of data. *
* This requires the index array provided by the program below. This *
* index should be generated at compile time not by the DSP. The code *
* is given below. *
* *
* TI retains all rights, title and interest in this code and only *
* authorizes the use of the bit-reversal code and related table *
* generation code with TMS320-family DSPs manufactured by TI. *
* *
* // ----------------------------------------------------------- // *
* // This routine calculates the index for bit reversal of // *
* // an array of length n. The length of the index table is // *
* // 2^(2*ceil(k/2)) where n = 2^k. // *
* // // *
* // In other words, the length of the index table is: // *
* // // *
* // Even power Odd Power // *
* // of radix of radix // *
* // sqrt(n) sqrt(2*n) // *
* // // *
* // ----------------------------------------------------------- // *
* void bitrev_index(short *index, int n) *
* { *
* int i, j, k, radix = 2; *
* short nbits, nbot, ntop, ndiff, n2, raddiv2; *
* *
* nbits = 0; *
* i = n; *
* while (i > 1) *
* { *
* i = i >> 1; *
* nbits++; *
* } *
* *
* raddiv2 = radix >> 1; *
* nbot = nbits >> raddiv2; *
* nbot = nbot << raddiv2 - 1; *
* ndiff = nbits & raddiv2; *
* ntop = nbot + ndiff; *
* n2 = 1 << ntop; *
* *
* index[0] = 0; *
* for ( i = 1, j = n2/radix + 1; i < n2 - 1; i++) *
* { *
* index[i] = j - 1; *
* *
* for (k = n2/radix; k*(radix-1) < j; k /= radix) *
* j -= k*(radix-1); *
* *
* j += k; *
* } *
* index[n2 - 1] = n2 - 1; *
* } *
* *
* C CODE *
* void bitrev(int *x, short *index, int nx) *
* { *
* int i; *
* short i0, i1, i2, i3; *
* short j0, j1, j2, j3; *
* int xi0, xi1, xi2, xi3; *
* int xj0, xj1, xj2, xj3; *
* short t; *
* int a, b, ia, ib, ibs; *
* int mask; *
* int nbits, nbot, ntop, ndiff, n2, halfn; *
* short *xs = (short *) x; *
* *
* nbits = 0; *
* i = nx; *
* while (i > 1) *
* { *
* i = i >> 1; *
* nbits++; *
* } *
* *
* nbot = nbits >> 1; *
* ndiff = nbits & 1; *
* ntop = nbot + ndiff; *
* n2 = 1 << ntop; *
* mask = n2 - 1; *
* halfn = nx >> 1; *
* *
* for (i0 = 0; i0 < halfn; i0 += 2) *
* { *
* b = i0 & mask; *
* a = i0 >> nbot; *
* if (!b) ia = index[a]; *
* ib = index[b]; *
* ibs = ib << nbot; *
* *
* j0 = ibs + ia; *
* t = i0 < j0; *
* xi0 = x[i0]; *
* xj0 = x[j0]; *
* *
* if (t){x[i0] = xj0; *
* x[j0] = xi0;} *
* *
* i1 = i0 + 1; *
* j1 = j0 + halfn; *
* xi1 = x[i1]; *
* xj1 = x[j1]; *
* x[i1] = xj1; *
* x[j1] = xi1; *
* *
* i3 = i1 + halfn; *
* j3 = j1 + 1; *
* xi3 = x[i3]; *
* xj3 = x[j3]; *
* if (t){x[i3] = xj3; *
* x[j3] = xi3;} *
* } *
* } *
* *
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