📄 gsm.c
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/* 4.2.2 Offset compensation
*
* This part implements a high-pass filter and requires extended
* arithmetic precision for the recursive part of this filter.
* The input of this procedure is the array so[0...159] and the
* output the array sof[ 0...159 ].
*/
/* Compute the non-recursive part
*/
s1 = SO - z1; /* s1 = gsm_sub( *so, z1 ); */
z1 = SO;
pgpAssert(s1 != MIN_WORD);
/* Compute the recursive part
*/
L_s2 = s1;
L_s2 <<= 15;
/* Execution of a 31 bv 16 bits multiplication
*/
msp = SASR( L_z2, 15 );
lsp = GSM_L_SUB(L_z2,(msp<<15));
L_s2 += GSM_MULT_R( lsp, 32735 );
L_temp = (longword)msp * 32735; /* GSM_L_MULT(msp,32735) >> 1;*/
L_z2 = GSM_L_ADD( L_temp, L_s2 );
/* Compute sof[k] with rounding
*/
L_temp = GSM_L_ADD( L_z2, 16384 );
/* 4.2.3 Preemphasis
*/
msp = GSM_MULT_R( mp, -28180 );
mp = SASR( L_temp, 15 );
*so++ = GSM_ADD( mp, msp );
}
S->z1 = z1;
S->L_z2 = L_z2;
S->mp = mp;
}
/*
* 4.2 FIXED POINT IMPLEMENTATION OF THE RPE-LTP CODER
*/
static void Gsm_Coder(
struct gsm_state * S,
word * s, /* [0..159] samples IN */
/*
* The RPE-LTD coder works on a frame by frame basis. The length of
* the frame is equal to 160 samples. Some computations are done
* once per frame to produce at the output of the coder the
* LARc[1..8] parameters which are the coded LAR coefficients and
* also to realize the inverse filtering operation for the entire
* frame (160 samples of signal d[0..159]). These parts produce at
* the output of the coder:
*/
word * LARc, /* [0..7] LAR coefficients OUT */
/*
* Procedure 4.2.11 to 4.2.18 are to be executed four times per
* frame. That means once for each sub-segment RPE-LTP analysis of
* 40 samples. These parts produce at the output of the coder:
*/
word * Nc, /* [0..3] LTP lag OUT */
word * bc, /* [0..3] coded LTP gain OUT */
word * Mc, /* [0..3] RPE grid selection OUT */
word * xmaxc,/* [0..3] Coded maximum amplitude OUT */
word * xMc /* [13*4] normalized RPE samples OUT */
)
{
int k;
word * dp = S->dp0 + 120; /* [ -120...-1 ] */
word * dpp = dp; /* [ 0...39 ] */
static word e [50] = {0};
word so[160];
Gsm_Preprocess (S, s, so);
Gsm_LPC_Analysis (so, LARc);
Gsm_Short_Term_Analysis_Filter (S, LARc, so);
for (k = 0; k <= 3; k++, xMc += 13) {
Gsm_Long_Term_Predictor ( S,
so+k*40, /* d [0..39] IN */
dp, /* dp [-120..-1] IN */
e + 5, /* e [0..39] OUT */
dpp, /* dpp [0..39] OUT */
Nc++,
bc++);
Gsm_RPE_Encoding (
e + 5, /* e ][0..39][ IN/OUT */
xmaxc++, Mc++, xMc );
/*
* Gsm_Update_of_reconstructed_short_time_residual_signal
* ( dpp, e + 5, dp );
*/
{ register int i;
for (i = 0; i <= 39; i++)
dp[ i ] = GSM_ADD( e[5 + i], dpp[i] );
}
dp += 40;
dpp += 40;
}
(void)memcpy( (char *)S->dp0, (char *)(S->dp0 + 160),
120 * sizeof(*S->dp0) );
}
/*
* 4.3 FIXED POINT IMPLEMENTATION OF THE RPE-LTP DECODER
*/
static void Postprocessing(
struct gsm_state * S,
register word * s)
{
register int k;
register word msr = S->msr;
register word tmp;
for (k = 160; k--; s++) {
tmp = GSM_MULT_R( msr, 28180 );
msr = GSM_ADD(*s, tmp); /* Deemphasis */
*s = GSM_ADD(msr, msr) & 0xFFF8; /* Truncation & Upscaling */
}
S->msr = msr;
}
static void Gsm_Decoder(
struct gsm_state * S,
word * LARcr, /* [0..7] IN */
word * Ncr, /* [0..3] IN */
word * bcr, /* [0..3] IN */
word * Mcr, /* [0..3] IN */
word * xmaxcr, /* [0..3] IN */
word * xMcr, /* [0..13*4] IN */
word * s) /* [0..159] OUT */
{
int j, k;
word erp[40], wt[160];
word * drp = S->dp0 + 120;
for (j=0; j <= 3; j++, xmaxcr++, bcr++, Ncr++, Mcr++, xMcr += 13) {
Gsm_RPE_Decoding( *xmaxcr, *Mcr, xMcr, erp );
Gsm_Long_Term_Synthesis_Filtering( S, *Ncr, *bcr, erp, drp );
for (k = 0; k <= 39; k++) wt[ j * 40 + k ] = drp[ k ];
}
Gsm_Short_Term_Synthesis_Filter( S, LARcr, wt, s );
Postprocessing(S, s);
}
/*
* 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 {
pgpAssert(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) {
pgpAssert(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;
}
pgpAssert( L_ACF[0] != 0 );
temp = gsm_norm( L_ACF[0] );
pgpAssert(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] );
pgpAssert(*r >= 0);
if (P[1] > 0) *r = -*r; /* r[n] = sub(0, r[n]) */
pgpAssert (*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);
pgpAssert(temp >= 0);
if (temp < 22118) {
temp >>= 1;
} else if (temp < 31130) {
pgpAssert( temp >= 11059 );
temp -= 11059;
} else {
pgpAssert( temp >= 26112 );
temp -= 26112;
temp <<= 2;
}
*r = *r < 0 ? -temp : temp;
pgpAssert( *r != MIN_WORD );
}
}
static void Gsm_LPC_Analysis(
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);
}
/* 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
}
/*
* SHORT TERM ANALYSIS FILTERING SECTION
*/
/* 4.2.8 */
static void Decoding_of_the_coded_Log_Area_Ratios(
word * LARc, /* coded log area ratio [0..7] IN */
word * LARpp) /* out: decoded .. */
{
register word temp1 /* , temp2 */;
/* register long ltmp; /* for GSM_ADD */
/* This procedure requires for efficient implementation
* two tables.
*
* INVA[1..8] = integer( (32768 * 8) / real_A[1..8])
* MIC[1..8] = minimum value of the LARc[1..8]
*/
/* Compute the LARpp[1..8]
*/
/* for (i = 1; i <= 8; i++, B++, MIC++, INVA++, LARc++, LARpp++) {
*
* temp1 = GSM_ADD( *LARc, *MIC ) << 10;
* temp2 = *B << 1;
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