FreeCalypso > hg > gsm-codec-lib
view libgsmfr2/lpc.c @ 495:aee13079db3c
libgsmhr1: implement SID reset
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 17 Jun 2024 23:25:19 +0000 |
parents | 0cfb7c95cce2 |
children |
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/* * This C source file has been adapted from TU-Berlin libgsm source, * original notice follows: * * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische * Universitaet Berlin. See the accompanying file "COPYRIGHT" for * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE. */ #include <stdint.h> #include <assert.h> #include "tw_gsmfr.h" #include "typedef.h" #include "ed_state.h" #include "ed_internal.h" /* * 4.2.4 .. 4.2.7 LPC ANALYSIS SECTION */ /* 4.2.4 */ static void Autocorrelation ( word * s, /* [0..159] IN/OUT */ longword * L_ACF) /* [0..8] OUT */ /* * The goal is to compute the array L_ACF[k]. The signal s[i] must * be scaled in order to avoid an overflow situation. */ { register int k, i; word temp, smax, scalauto; /* Dynamic scaling of the array s[0..159] */ /* Search for the maximum. */ smax = 0; for (k = 0; k <= 159; k++) { temp = GSM_ABS( s[k] ); if (temp > smax) smax = temp; } /* Computation of the scaling factor. */ if (smax == 0) scalauto = 0; else { assert(smax > 0); scalauto = 4 - gsm_norm( (longword)smax << 16 );/* sub(4,..) */ } /* Scaling of the array s[0...159] */ if (scalauto > 0) { # define SCALE(n) \ case n: for (k = 0; k <= 159; k++) \ s[k] = GSM_MULT_R( s[k], 16384 >> (n-1) );\ break; switch (scalauto) { SCALE(1) SCALE(2) SCALE(3) SCALE(4) } # undef SCALE } /* Compute the L_ACF[..]. */ { word * sp = s; word sl = *sp; # define STEP(k) L_ACF[k] += ((longword)sl * sp[ -(k) ]); # define NEXTI sl = *++sp for (k = 9; k--; L_ACF[k] = 0) ; STEP (0); NEXTI; STEP(0); STEP(1); NEXTI; STEP(0); STEP(1); STEP(2); NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); STEP(7); for (i = 8; i <= 159; i++) { NEXTI; STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); STEP(7); STEP(8); } for (k = 9; k--; L_ACF[k] <<= 1) ; } /* Rescaling of the array s[0..159] */ if (scalauto > 0) { assert(scalauto <= 4); for (k = 160; k--; *s++ <<= scalauto) ; } } /* 4.2.5 */ static void Reflection_coefficients ( longword * L_ACF, /* 0...8 IN */ register word * r /* 0...7 OUT */ ) { register int i, m, n; register word temp; register longword ltmp; word ACF[9]; /* 0..8 */ word P[ 9]; /* 0..8 */ word K[ 9]; /* 2..8 */ /* Schur recursion with 16 bits arithmetic. */ if (L_ACF[0] == 0) { for (i = 8; i--; *r++ = 0) ; return; } assert( L_ACF[0] != 0 ); temp = gsm_norm( L_ACF[0] ); assert(temp >= 0 && temp < 32); /* ? overflow ? */ for (i = 0; i <= 8; i++) ACF[i] = SASR( L_ACF[i] << temp, 16 ); /* Initialize array P[..] and K[..] for the recursion. */ for (i = 1; i <= 7; i++) K[ i ] = ACF[ i ]; for (i = 0; i <= 8; i++) P[ i ] = ACF[ i ]; /* Compute reflection coefficients */ for (n = 1; n <= 8; n++, r++) { temp = P[1]; temp = GSM_ABS(temp); if (P[0] < temp) { for (i = n; i <= 8; i++) *r++ = 0; return; } *r = gsm_div( temp, P[0] ); assert(*r >= 0); if (P[1] > 0) *r = -*r; /* r[n] = sub(0, r[n]) */ assert (*r != MIN_WORD); if (n == 8) return; /* Schur recursion */ temp = GSM_MULT_R( P[1], *r ); P[0] = GSM_ADD( P[0], temp ); for (m = 1; m <= 8 - n; m++) { temp = GSM_MULT_R( K[ m ], *r ); P[m] = GSM_ADD( P[ m+1 ], temp ); temp = GSM_MULT_R( P[ m+1 ], *r ); K[m] = GSM_ADD( K[ m ], temp ); } } } /* 4.2.6 */ static void Transformation_to_Log_Area_Ratios ( register word * r /* 0..7 IN/OUT */ ) /* * The following scaling for r[..] and LAR[..] has been used: * * r[..] = integer( real_r[..]*32768. ); -1 <= real_r < 1. * LAR[..] = integer( real_LAR[..] * 16384 ); * with -1.625 <= real_LAR <= 1.625 */ { register word temp; register int i; /* Computation of the LAR[0..7] from the r[0..7] */ for (i = 1; i <= 8; i++, r++) { temp = *r; temp = GSM_ABS(temp); assert(temp >= 0); if (temp < 22118) { temp >>= 1; } else if (temp < 31130) { assert( temp >= 11059 ); temp -= 11059; } else { assert( temp >= 26112 ); temp -= 26112; temp <<= 2; } *r = *r < 0 ? -temp : temp; assert( *r != MIN_WORD ); } } /* 4.2.7 */ static void Quantization_and_coding ( register word * LAR /* [0..7] IN/OUT */ ) { register word temp; longword ltmp; /* This procedure needs four tables; the following equations * give the optimum scaling for the constants: * * A[0..7] = integer( real_A[0..7] * 1024 ) * B[0..7] = integer( real_B[0..7] * 512 ) * MAC[0..7] = maximum of the LARc[0..7] * MIC[0..7] = minimum of the LARc[0..7] */ # undef STEP # define STEP( A, B, MAC, MIC ) \ temp = GSM_MULT( A, *LAR ); \ temp = GSM_ADD( temp, B ); \ temp = GSM_ADD( temp, 256 ); \ temp = SASR( temp, 9 ); \ *LAR = temp>MAC ? MAC - MIC : (temp<MIC ? 0 : temp - MIC); \ LAR++; STEP( 20480, 0, 31, -32 ); STEP( 20480, 0, 31, -32 ); STEP( 20480, 2048, 15, -16 ); STEP( 20480, -2560, 15, -16 ); STEP( 13964, 94, 7, -8 ); STEP( 15360, -1792, 7, -8 ); STEP( 8534, -341, 3, -4 ); STEP( 9036, -1144, 3, -4 ); # undef STEP } void Gsm_LPC_Analysis ( struct gsmfr_0610_state *S, word * s, /* 0..159 signals IN/OUT */ word * LARc) /* 0..7 LARc's OUT */ { longword L_ACF[9]; Autocorrelation (s, L_ACF ); Reflection_coefficients (L_ACF, LARc ); Transformation_to_Log_Area_Ratios (LARc); Quantization_and_coding (LARc); }