2 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
3 * Universitaet Berlin. See the accompanying file "COPYRIGHT" for
4 * details. THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
20 * 4.2.4 .. 4.2.7 LPC ANALYSIS SECTION
26 static void Autocorrelation P2((s, L_ACF),
27 word * s, /* [0..159] IN/OUT */
28 longword * L_ACF) /* [0..8] OUT */
30 * The goal is to compute the array L_ACF[k]. The signal s[i] must
31 * be scaled in order to avoid an overflow situation.
36 word temp, smax, scalauto;
42 /* Dynamic scaling of the array s[0..159]
45 /* Search for the maximum.
48 for (k = 0; k <= 159; k++) {
49 temp = GSM_ABS( s[k] );
50 if (temp > smax) smax = temp;
53 /* Computation of the scaling factor.
55 if (smax == 0) scalauto = 0;
58 scalauto = 4 - gsm_norm( (longword)smax << 16 );/* sub(4,..) */
61 /* Scaling of the array s[0...159]
68 case n: for (k = 0; k <= 159; k++) \
69 float_s[k] = (float) \
70 (s[k] = GSM_MULT_R(s[k], 16384 >> (n-1)));\
74 case n: for (k = 0; k <= 159; k++) \
75 s[k] = GSM_MULT_R( s[k], 16384 >> (n-1) );\
77 # endif /* USE_FLOAT_MUL */
88 else for (k = 0; k <= 159; k++) float_s[k] = (float) s[k];
91 /* Compute the L_ACF[..].
95 register float * sp = float_s;
96 register float sl = *sp;
98 # define STEP(k) L_ACF[k] += (longword)(sl * sp[ -(k) ]);
103 # define STEP(k) L_ACF[k] += ((longword)sl * sp[ -(k) ]);
106 # define NEXTI sl = *++sp
109 for (k = 9; k--; L_ACF[k] = 0) ;
115 STEP(0); STEP(1); STEP(2);
117 STEP(0); STEP(1); STEP(2); STEP(3);
119 STEP(0); STEP(1); STEP(2); STEP(3); STEP(4);
121 STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5);
123 STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6);
125 STEP(0); STEP(1); STEP(2); STEP(3); STEP(4); STEP(5); STEP(6); STEP(7);
127 for (i = 8; i <= 159; i++) {
132 STEP(1); STEP(2); STEP(3); STEP(4);
133 STEP(5); STEP(6); STEP(7); STEP(8);
136 for (k = 9; k--; L_ACF[k] <<= 1) ;
139 /* Rescaling of the array s[0..159]
142 assert(scalauto <= 4);
143 for (k = 160; k--; *s++ <<= scalauto) ;
147 #if defined(USE_FLOAT_MUL) && defined(FAST)
149 static void Fast_Autocorrelation P2((s, L_ACF),
150 word * s, /* [0..159] IN/OUT */
151 longword * L_ACF) /* [0..8] OUT */
158 register float *sf = s_f;
160 for (i = 0; i < 160; ++i) sf[i] = s[i];
161 for (k = 0; k <= 8; k++) {
162 register float L_temp2 = 0;
163 register float *sfl = sf - k;
164 for (i = k; i < 160; ++i) L_temp2 += sf[i] * sfl[i];
165 f_L_ACF[k] = L_temp2;
167 scale = MAX_LONGWORD / f_L_ACF[0];
169 for (k = 0; k <= 8; k++) {
170 L_ACF[k] = f_L_ACF[k] * scale;
173 #endif /* defined (USE_FLOAT_MUL) && defined (FAST) */
177 static void Reflection_coefficients P2( (L_ACF, r),
178 longword * L_ACF, /* 0...8 IN */
179 register word * r /* 0...7 OUT */
182 register int i, m, n;
184 register longword ltmp;
185 word ACF[9]; /* 0..8 */
186 word P[ 9]; /* 0..8 */
187 word K[ 9]; /* 2..8 */
189 /* Schur recursion with 16 bits arithmetic.
193 for (i = 8; i--; *r++ = 0) ;
197 assert( L_ACF[0] != 0 );
198 temp = gsm_norm( L_ACF[0] );
200 assert(temp >= 0 && temp < 32);
203 for (i = 0; i <= 8; i++) ACF[i] = SASR( L_ACF[i] << temp, 16 );
205 /* Initialize array P[..] and K[..] for the recursion.
208 for (i = 1; i <= 7; i++) K[ i ] = ACF[ i ];
209 for (i = 0; i <= 8; i++) P[ i ] = ACF[ i ];
211 /* Compute reflection coefficients
213 for (n = 1; n <= 8; n++, r++) {
216 temp = GSM_ABS(temp);
218 for (i = n; i <= 8; i++) *r++ = 0;
222 *r = gsm_div( temp, P[0] );
225 if (P[1] > 0) *r = -*r; /* r[n] = sub(0, r[n]) */
226 assert (*r != MIN_WORD);
231 temp = GSM_MULT_R( P[1], *r );
232 P[0] = GSM_ADD( P[0], temp );
234 for (m = 1; m <= 8 - n; m++) {
235 temp = GSM_MULT_R( K[ m ], *r );
236 P[m] = GSM_ADD( P[ m+1 ], temp );
238 temp = GSM_MULT_R( P[ m+1 ], *r );
239 K[m] = GSM_ADD( K[ m ], temp );
246 static void Transformation_to_Log_Area_Ratios P1((r),
247 register word * r /* 0..7 IN/OUT */
250 * The following scaling for r[..] and LAR[..] has been used:
252 * r[..] = integer( real_r[..]*32768. ); -1 <= real_r < 1.
253 * LAR[..] = integer( real_LAR[..] * 16384 );
254 * with -1.625 <= real_LAR <= 1.625
261 /* Computation of the LAR[0..7] from the r[0..7]
263 for (i = 1; i <= 8; i++, r++) {
266 temp = GSM_ABS(temp);
271 } else if (temp < 31130) {
272 assert( temp >= 11059 );
275 assert( temp >= 26112 );
280 *r = *r < 0 ? -temp : temp;
281 assert( *r != MIN_WORD );
287 static void Quantization_and_coding P1((LAR),
288 register word * LAR /* [0..7] IN/OUT */
295 /* This procedure needs four tables; the following equations
296 * give the optimum scaling for the constants:
298 * A[0..7] = integer( real_A[0..7] * 1024 )
299 * B[0..7] = integer( real_B[0..7] * 512 )
300 * MAC[0..7] = maximum of the LARc[0..7]
301 * MIC[0..7] = minimum of the LARc[0..7]
305 # define STEP( A, B, MAC, MIC ) \
306 temp = GSM_MULT( A, *LAR ); \
307 temp = GSM_ADD( temp, B ); \
308 temp = GSM_ADD( temp, 256 ); \
309 temp = SASR( temp, 9 ); \
310 *LAR = temp>MAC ? MAC - MIC : (temp<MIC ? 0 : temp - MIC); \
313 STEP( 20480, 0, 31, -32 );
314 STEP( 20480, 0, 31, -32 );
315 STEP( 20480, 2048, 15, -16 );
316 STEP( 20480, -2560, 15, -16 );
318 STEP( 13964, 94, 7, -8 );
319 STEP( 15360, -1792, 7, -8 );
320 STEP( 8534, -341, 3, -4 );
321 STEP( 9036, -1144, 3, -4 );
326 void Gsm_LPC_Analysis P3((S, s,LARc),
328 word * s, /* 0..159 signals IN/OUT */
329 word * LARc) /* 0..7 LARc's OUT */
333 #if defined(USE_FLOAT_MUL) && defined(FAST)
334 if (S->fast) Fast_Autocorrelation (s, L_ACF );
337 Autocorrelation (s, L_ACF );
338 Reflection_coefficients (L_ACF, LARc );
339 Transformation_to_Log_Area_Ratios (LARc);
340 Quantization_and_coding (LARc);