/* ======================================================================== */ /* TEXAS INSTRUMENTS, INC. */ /* */ /* NAME */ /* tw_radix2 */ /* */ /* USAGE */ /* This is a stand-alone program intended to generate twiddle-factor */ /* arrays for the DSP_radix2 FFT library routine. It is called as */ /* follows: */ /* */ /* tw_radix2 [-s scale] N > outputfile.c */ /* */ /* The argument 'N' specifies the size of the FFT. This value */ /* must be a power of 2. The switch '-s scale' allows selecting */ /* a different scale factor for the coefficients. The default */ /* scale factor is 32767.5. */ /* */ /* This program will generate the twiddle factor array 'w' and */ /* output the result to the display. Redirect the output to */ /* a file as shown above. */ /* */ /* DESCRIPTION */ /* This program contains the twiddle-factor generation routine */ /* that is described within the source code for the DSPLIB */ /* FFT function DSP_radix2. It does not produce appropriate */ /* twiddle-factor arrays for the other FFT implementations. */ /* */ /* Please consult the specific FFT that you are using for details. */ /* */ /* The final twiddle-factor array generated by the routine will */ /* be 2 * N elements long. */ /* */ /* NOTES */ /* The code below may be adapted to run directly on the target, */ /* rather than running as a separate program running off-line. */ /* Such adaptation is not recommended for time-critical applications. */ /* To adapt this program, remove the 'usage' and 'main' functions, */ /* and call 'gen_twiddle' directly. */ /* */ /* ------------------------------------------------------------------------ */ /* Copyright (c) 2001 Texas Instruments, Incorporated. */ /* All Rights Reserved. */ /* ======================================================================== */ #include #include #include #include #include #ifndef PI # ifdef M_PI # define PI M_PI # else # define PI 3.14159265358979323846 # endif #endif /* ======================================================================== */ /* D2S -- Truncate a 'double' to a 'short', with clamping. */ /* ======================================================================== */ static short d2s(double d) { if (d >= 32767.0) return 32767; if (d <= -32768.0) return -32768; return (short)d; } /* ======================================================================== */ /* GEN_TWIDDLE -- Generate twiddle factors for TI's custom FFTs. */ /* */ /* USAGE */ /* This routine is called as follows: */ /* */ /* int gen_twiddle(short *w, int n, double scale) */ /* */ /* short *w Pointer to twiddle-factor array */ /* int n Size of FFT */ /* double scale Scale factor to apply to values. */ /* */ /* The routine will generate the twiddle-factors directly into the */ /* array you specify. The array needs to be N elements long. */ /* ======================================================================== */ int gen_twiddle(short *w, int n, double scale) { double angle, step; int i; step = (2.0 * PI) / (double)n; for (i = 0, angle = 0.0; i < n; i += 2, angle += step) { w[i + 0] = d2s(scale * -cos(angle)); w[i + 1] = d2s(scale * -sin(angle)); } return n; } /* ======================================================================== */ /* USAGE -- Print usage information and optionally an error message. */ /* ======================================================================== */ void usage(char *error) { fprintf(stderr, " \n" "USAGE \n" " This is a stand-alone program intended to generate twiddle-factor \n" " arrays for the DSP_radix2 library routine. It is called as follows:\n" " \n" " tw_radix2 [-s scale] N > outputfile.c \n" " \n" " The argument 'N' specifies the size of the FFT. This value \n" " must be a power of 2. The switch '-s scale' allows selecting \n" " a different scale factor for the coefficients. The default \n" " scale factor is 32767.5. \n" " \n" " This program will generate the twiddle factor array 'w' and \n" " output the result to the display. Redirect the output to \n" " a file as shown above. \n" " \n"); if (error) fprintf(stderr, "ERROR: %s\n", error); exit(1); } /* ======================================================================== */ /* MAIN -- Where the action happens. */ /* ======================================================================== */ int main(int argc, char *argv[]) { int i, n = -1, size; int is_pow_4 = 0; short *w; double scale = 32767.5; char *s; char buf[80]; /* -------------------------------------------------------------------- */ /* Parse the arguments. */ /* -------------------------------------------------------------------- */ if (argc < 2) { usage(NULL); } while (argc-->1) { if (**++argv == '-' || **argv == '/') { switch (argv[0][1]) { case 's' : case 'S' : { if (argv[0][2]) { s = &argv[0][2]; } else { argc--; s = *++argv; } if (!s || !*s || sscanf(s, "%lf", &scale) != 1) usage("The -s switch requires a numeric argument.\n"); if (scale <= 0.0 || scale > 32767.6) usage("Scale factor out of range.\n"); break; } default: { sprintf(buf, "Unrecognized switch character: '%c'\n", argv[0][1]); usage(buf); break; } } } else { if (!isdigit(argv[0][0]) || sscanf(argv[0], "%d", &n) != 1) { sprintf(buf, "Unrecognized argument: %-.32s\n", argv[0][0]); usage(buf); } if (n < 16 || n > 32768) usage("FFT size must be between 16 and 32768 points."); for (i = 2; i < 24; i++) if ((1 << i) == n) break; is_pow_4 = !(i & 1); if (i >= 24) { usage("FFT size must be a power of 2\n"); exit(1); } } } if (n == -1) usage("Must specify FFT size."); /* -------------------------------------------------------------------- */ /* Allocate memory for the FFT twiddle factors. */ /* -------------------------------------------------------------------- */ w = calloc(2 * sizeof(short), n); if (!w) { fprintf(stderr, "ERROR: Unable to allocate memory for " "twiddle factors\n"); exit(1); } /* -------------------------------------------------------------------- */ /* Generate the twiddle-factor array. */ /* -------------------------------------------------------------------- */ size = gen_twiddle(w, n, scale); /* -------------------------------------------------------------------- */ /* Print out the resulting twiddle factors. */ /* -------------------------------------------------------------------- */ printf( "/* -------------------------------------------------------------------- */\n" "/* Automatically generated twiddle-factor array. */\n" "/* Number of points: %-5d */\n" "/* Scale factor: %-20.9f */\n" "/* Appropriate FFTs: DSP_radix2 */\n" "/* Required alignment: 4 byte (word) */\n" "/* -------------------------------------------------------------------- */\n" "/* NOTE: It is suggested that this array be aligned in a different */\n" "/* starting bank than the actual FFT data, to reduce bank conflicts. */\n" "/* This can be achieved by using the DATA_MEM_BANK pragma. Please */\n" "/* see the TMS320C6000 Optimizing C Compiler Reference (SPRU187E) */\n" "/* for details on \"#pragma DATA_MEM_BANK\". */\n" "/* -------------------------------------------------------------------- */\n" "\n" "#pragma DATA_ALIGN(w, 4); /* Remove this if using DATA_MEM_BANK */\n" "\n", n, scale); printf("const short w[2 * %d] =\n{", size / 2); for (i = 0; i < size; i++) { printf("%s%c0x%.4X", i == 0 ? "\n " : (i & 7) == 0 ? ",\n " : ", ", w[i] < 0 ? '-' : ' ', abs(w[i])); } printf("\n};\n"); return 0; }