blob: 21a8f40df6f16f7cca25a3b6cf5f4195d9dab08c [file] [log] [blame]
 /* * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved. * * Use of this source code is governed by a BSD-style license * that can be found in the LICENSE file in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. */ /****************************************************************** iLBC Speech Coder ANSI-C Source Code WebRtcIlbcfix_Chebyshev.c ******************************************************************/ #include "defines.h" #include "constants.h" /*------------------------------------------------------------------* * Calculate the Chevyshev polynomial series * F(w) = 2*exp(-j5w)*C(x) * C(x) = (T_0(x) + f(1)T_1(x) + ... + f(4)T_1(x) + f(5)/2) * T_i(x) is the i:th order Chebyshev polynomial *------------------------------------------------------------------*/ int16_t WebRtcIlbcfix_Chebyshev( /* (o) Result of C(x) */ int16_t x, /* (i) Value to the Chevyshev polynomial */ int16_t *f /* (i) The coefficients in the polynomial */ ) { int16_t b1_high, b1_low; /* Use the high, low format to increase the accuracy */ int32_t b2; int32_t tmp1W32; int32_t tmp2W32; int i; b2 = (int32_t)0x1000000; /* b2 = 1.0 (Q23) */ /* Calculate b1 = 2*x + f[1] */ tmp1W32 = (x << 10) + (f[1] << 14); for (i = 2; i < 5; i++) { tmp2W32 = tmp1W32; /* Split b1 (in tmp1W32) into a high and low part */ b1_high = (int16_t)(tmp1W32 >> 16); b1_low = (int16_t)((tmp1W32 - ((int32_t)b1_high << 16)) >> 1); /* Calculate 2*x*b1-b2+f[i] */ tmp1W32 = ((b1_high * x + ((b1_low * x) >> 15)) << 2) - b2 + (f[i] << 14); /* Update b2 for next round */ b2 = tmp2W32; } /* Split b1 (in tmp1W32) into a high and low part */ b1_high = (int16_t)(tmp1W32 >> 16); b1_low = (int16_t)((tmp1W32 - ((int32_t)b1_high << 16)) >> 1); /* tmp1W32 = x*b1 - b2 + f[i]/2 */ tmp1W32 = ((b1_high * x) << 1) + (((b1_low * x) >> 15) << 1) - b2 + (f[i] << 13); /* Handle overflows and set to maximum or minimum int16_t instead */ if (tmp1W32>((int32_t)33553408)) { return(WEBRTC_SPL_WORD16_MAX); } else if (tmp1W32<((int32_t)-33554432)) { return(WEBRTC_SPL_WORD16_MIN); } else { return (int16_t)(tmp1W32 >> 10); } }