| 514 | } |
| 515 | |
| 516 | void fftBRInit(int M, int16_t * BRLow) |
| 517 | { |
| 518 | /* Compute BRLow, the bit reversed table for ffts */ |
| 519 | /* of size pow(2,M/2 -1) */ |
| 520 | /* INPUTS */ |
| 521 | /* M = log2 of fft size */ |
| 522 | /* OUTPUTS */ |
| 523 | /* *BRLow = bit reversed counter table */ |
| 524 | int Mroot_1 = M / 2 - 1; |
| 525 | int Nroot_1 = POW2(Mroot_1); |
| 526 | int i1; |
| 527 | int bitsum; |
| 528 | int bitmask; |
| 529 | int bit; |
| 530 | |
| 531 | for (i1 = 0; i1 < Nroot_1; i1++) |
| 532 | { |
| 533 | bitsum = 0; |
| 534 | bitmask = 1; |
| 535 | for (bit = 1; bit <= Mroot_1; bitmask <<= 1, bit++) |
| 536 | if (i1 & bitmask) |
| 537 | bitsum = bitsum + (Nroot_1 >> bit); |
| 538 | BRLow[i1] = bitsum; |
| 539 | } |
| 540 | } |
| 541 | |
| 542 | /***************** |
| 543 | * parts of ffts1 * |