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 /* * 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 *------------------------------------------------------------------*/ WebRtc_Word16 WebRtcIlbcfix_Chebyshev( /* (o) Result of C(x) */ WebRtc_Word16 x, /* (i) Value to the Chevyshev polynomial */ WebRtc_Word16 *f /* (i) The coefficients in the polynomial */ ) { WebRtc_Word16 b1_high, b1_low; /* Use the high, low format to increase the accuracy */ WebRtc_Word32 b2; WebRtc_Word32 tmp1W32; WebRtc_Word32 tmp2W32; int i; b2 = (WebRtc_Word32)0x1000000; /* b2 = 1.0 (Q23) */ /* Calculate b1 = 2*x + f[1] */ tmp1W32 = WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)x, 10); tmp1W32 += WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)f[1], 14); for (i = 2; i < 5; i++) { tmp2W32 = tmp1W32; /* Split b1 (in tmp1W32) into a high and low part */ b1_high = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp1W32, 16); b1_low = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp1W32-WEBRTC_SPL_LSHIFT_W32(((WebRtc_Word32)b1_high),16), 1); /* Calculate 2*x*b1-b2+f[i] */ tmp1W32 = WEBRTC_SPL_LSHIFT_W32( (WEBRTC_SPL_MUL_16_16(b1_high, x) + WEBRTC_SPL_MUL_16_16_RSFT(b1_low, x, 15)), 2); tmp1W32 -= b2; tmp1W32 += WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)f[i], 14); /* Update b2 for next round */ b2 = tmp2W32; } /* Split b1 (in tmp1W32) into a high and low part */ b1_high = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp1W32, 16); b1_low = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp1W32-WEBRTC_SPL_LSHIFT_W32(((WebRtc_Word32)b1_high),16), 1); /* tmp1W32 = x*b1 - b2 + f[i]/2 */ tmp1W32 = WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16(b1_high, x), 1) + WEBRTC_SPL_LSHIFT_W32(WEBRTC_SPL_MUL_16_16_RSFT(b1_low, x, 15), 1); tmp1W32 -= b2; tmp1W32 += WEBRTC_SPL_LSHIFT_W32((WebRtc_Word32)f[i], 13); /* Handle overflows and set to maximum or minimum WebRtc_Word16 instead */ if (tmp1W32>((WebRtc_Word32)33553408)) { return(WEBRTC_SPL_WORD16_MAX); } else if (tmp1W32<((WebRtc_Word32)-33554432)) { return(WEBRTC_SPL_WORD16_MIN); } else { return((WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32(tmp1W32, 10)); } }