Texas Instruments TMS320C67 DSP Series Programmer's Reference Manual page 57

DSPF_sp_ifftSPxSP
Benchmarks
4-32
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The data produced by the DSPF_sp_ifftSPxSP ifft is in normal form, the
whole data array is written into a new output buffer.
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The DSPF_sp_ifftSPxSP butterfly is bit reversed, i.e., the inner 2 points
of the butterfly are crossed over, this has the effect of making the data
come out in bit reversed rather than DSPF_sp_ifftSPxSP digit reversed or-
der. This simplifies the last pass of the loop. ia simple table is used to do
the bit reversal out of place.
unsigned char brev[64] = {
0x0, 0x20, 0x10, 0x30, 0x8, 0x28, 0x18, 0x38,
0x4, 0x24, 0x14, 0x34, 0xc, 0x2c, 0x1c, 0x3c,
0x2, 0x22, 0x12, 0x32, 0xa, 0x2a, 0x1a, 0x3a,
0x6, 0x26, 0x16, 0x36, 0xe, 0x2e, 0x1e, 0x3e,
0x1, 0x21, 0x11, 0x31, 0x9, 0x29, 0x19, 0x39,
0x5, 0x25, 0x15, 0x35, 0xd, 0x2d, 0x1d, 0x3d,
0x3, 0x23, 0x13, 0x33, 0xb, 0x2b, 0x1b, 0x3b,
0x7, 0x27, 0x17, 0x37, 0xf, 0x2f, 0x1f, 0x3f
};
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The special sequence of twiddle factors w can be generated using the
tw_fftSPxSP_C67
fft\tw_fftSPxSP_C67.c file or by running tw_fftSPxSP_C67.exe in
dsplib\bin.
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The brev table required for this function is provided in the file dsplib\sup-
port\fft\brev_table.h.
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Endianess: Configuration is little endian.
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Interruptibility: An interruptible window of 1 cycle is available between
the 2 outer loops.
Cycles cycles = 3 * ceil(log4(N)-1) * N + 21*ceil(log4(N)-1) + 2*N +
44
e.g., N = 1024, cycles = 14464
e.g., N = 512, cycles = 7296
e.g., N = 256, cycles = 2923
e.g., N = 128, cycles = 1515
e.g., N = 64, cycles = 598
Code size 1472
(in bytes)
function provided in the dsplib\support\