?? lpc.c
字號(hào):
/*-------------------------------------------------------------*
* procedure Az_lsp: *
* ~~~~~~ *
* Compute the LSPs from the LPC coefficients (order=10) *
*-------------------------------------------------------------*/
/* local function */
static Word16 Chebps_11(Word16 x, Word16 f[], Word16 n);
static Word16 Chebps_10(Word16 x, Word16 f[], Word16 n);
void Az_lsp(
Word16 a[], /* (i) Q12 : predictor coefficients */
Word16 lsp[], /* (o) Q15 : line spectral pairs */
Word16 old_lsp[] /* (i) : old lsp[] (in case not found 10 roots) */
)
{
Word16 i, j, nf, ip;
Word16 xlow, ylow, xhigh, yhigh, xmid, ymid, xint;
Word16 x, y, sign, exp;
Word16 *coef;
Word16 f1[M/2+1], f2[M/2+1];
Word32 t0, L_temp;
Flag ovf_coef;
Word16 (*pChebps)(Word16 x, Word16 f[], Word16 n);
/*-------------------------------------------------------------*
* find the sum and diff. pol. F1(z) and F2(z) *
* F1(z) <--- F1(z)/(1+z**-1) & F2(z) <--- F2(z)/(1-z**-1) *
* *
* f1[0] = 1.0; *
* f2[0] = 1.0; *
* *
* for (i = 0; i< NC; i++) *
* { *
* f1[i+1] = a[i+1] + a[M-i] - f1[i] ; *
* f2[i+1] = a[i+1] - a[M-i] + f2[i] ; *
* } *
*-------------------------------------------------------------*/
ovf_coef = 0;
pChebps = Chebps_11;
f1[0] = 2048; /* f1[0] = 1.0 is in Q11 */
f2[0] = 2048; /* f2[0] = 1.0 is in Q11 */
for (i = 0; i< NC; i++)
{
Overflow = 0;
t0 = L_mult(a[i+1], 16384); /* x = (a[i+1] + a[M-i]) >> 1 */
t0 = L_mac(t0, a[M-i], 16384); /* -> From Q12 to Q11 */
x = extract_h(t0);
if ( Overflow ) {
ovf_coef = 1; }
Overflow = 0;
f1[i+1] = sub(x, f1[i]); /* f1[i+1] = a[i+1] + a[M-i] - f1[i] */
if ( Overflow ) {
ovf_coef = 1; }
Overflow = 0;
t0 = L_mult(a[i+1], 16384); /* x = (a[i+1] - a[M-i]) >> 1 */
t0 = L_msu(t0, a[M-i], 16384); /* -> From Q12 to Q11 */
x = extract_h(t0);
if ( Overflow ) {
ovf_coef = 1; }
Overflow = 0;
f2[i+1] = add(x, f2[i]); /* f2[i+1] = a[i+1] - a[M-i] + f2[i] */
if ( Overflow ) {
ovf_coef = 1; }
}
if ( ovf_coef ) {
/*printf("===== OVF ovf_coef =====\n");*/
pChebps = Chebps_10;
f1[0] = 1024; /* f1[0] = 1.0 is in Q10 */
f2[0] = 1024; /* f2[0] = 1.0 is in Q10 */
for (i = 0; i< NC; i++)
{
t0 = L_mult(a[i+1], 8192); /* x = (a[i+1] + a[M-i]) >> 1 */
t0 = L_mac(t0, a[M-i], 8192); /* -> From Q11 to Q10 */
x = extract_h(t0);
f1[i+1] = sub(x, f1[i]); /* f1[i+1] = a[i+1] + a[M-i] - f1[i] */
t0 = L_mult(a[i+1], 8192); /* x = (a[i+1] - a[M-i]) >> 1 */
t0 = L_msu(t0, a[M-i], 8192); /* -> From Q11 to Q10 */
x = extract_h(t0);
f2[i+1] = add(x, f2[i]); /* f2[i+1] = a[i+1] - a[M-i] + f2[i] */
}
}
/*-------------------------------------------------------------*
* find the LSPs using the Chebichev pol. evaluation *
*-------------------------------------------------------------*/
nf=0; /* number of found frequencies */
ip=0; /* indicator for f1 or f2 */
coef = f1;
xlow = grid[0];
ylow = (*pChebps)(xlow, coef, NC);
j = 0;
while ( (nf < M) && (j < GRID_POINTS) )
{
j =add(j,1);
xhigh = xlow;
yhigh = ylow;
xlow = grid[j];
ylow = (*pChebps)(xlow,coef,NC);
L_temp = L_mult(ylow ,yhigh);
if ( L_temp <= (Word32)0)
{
/* divide 4 times the interval */
for (i = 0; i < 4; i++)
{
xmid = add( shr(xlow, 1) , shr(xhigh, 1)); /* xmid = (xlow + xhigh)/2 */
ymid = (*pChebps)(xmid,coef,NC);
L_temp = L_mult(ylow,ymid);
if ( L_temp <= (Word32)0)
{
yhigh = ymid;
xhigh = xmid;
}
else
{
ylow = ymid;
xlow = xmid;
}
}
/*-------------------------------------------------------------*
* Linear interpolation *
* xint = xlow - ylow*(xhigh-xlow)/(yhigh-ylow); *
*-------------------------------------------------------------*/
x = sub(xhigh, xlow);
y = sub(yhigh, ylow);
if(y == 0)
{
xint = xlow;
}
else
{
sign= y;
y = abs_s(y);
exp = norm_s(y);
y = shl(y, exp);
y = div_s( (Word16)16383, y);
t0 = L_mult(x, y);
t0 = L_shr(t0, sub(20, exp) );
y = extract_l(t0); /* y= (xhigh-xlow)/(yhigh-ylow) in Q11 */
if(sign < 0) y = negate(y);
t0 = L_mult(ylow, y); /* result in Q26 */
t0 = L_shr(t0, 11); /* result in Q15 */
xint = sub(xlow, extract_l(t0)); /* xint = xlow - ylow*y */
}
lsp[nf] = xint;
xlow = xint;
nf =add(nf,1);
if(ip == 0)
{
ip = 1;
coef = f2;
}
else
{
ip = 0;
coef = f1;
}
ylow = (*pChebps)(xlow,coef,NC);
}
}
/* Check if M roots found */
if( sub(nf, M) < 0)
{
for(i=0; i<M; i++)
{
lsp[i] = old_lsp[i];
}
/* printf("\n !!Not 10 roots found in Az_lsp()!!!\n"); */
}
return;
}
/*--------------------------------------------------------------*
* function Chebps_11, Chebps_10: *
* ~~~~~~~~~~~~~~~~~~~~ *
* Evaluates the Chebichev polynomial series *
*--------------------------------------------------------------*
* *
* The polynomial order is *
* n = M/2 (M is the prediction order) *
* The polynomial is given by *
* C(x) = T_n(x) + f(1)T_n-1(x) + ... +f(n-1)T_1(x) + f(n)/2 *
* Arguments: *
* x: input value of evaluation; x = cos(frequency) in Q15 *
* f[]: coefficients of the pol. *
* in Q11(Chebps_11), in Q10(Chebps_10) *
* n: order of the pol. *
* *
* The value of C(x) is returned. (Saturated to +-1.99 in Q14) *
* *
*--------------------------------------------------------------*/
static Word16 Chebps_11(Word16 x, Word16 f[], Word16 n)
{
Word16 i, cheb;
Word16 b0_h, b0_l, b1_h, b1_l, b2_h, b2_l;
Word32 t0;
/* Note: All computation are done in Q24. */
b2_h = 256; /* b2 = 1.0 in Q24 DPF */
b2_l = 0;
t0 = L_mult(x, 512); /* 2*x in Q24 */
t0 = L_mac(t0, f[1], 4096); /* + f[1] in Q24 */
L_Extract(t0, &b1_h, &b1_l); /* b1 = 2*x + f[1] */
for (i = 2; i<n; i++)
{
t0 = Mpy_32_16(b1_h, b1_l, x); /* t0 = 2.0*x*b1 */
t0 = L_shl(t0, 1);
t0 = L_mac(t0,b2_h,(Word16)-32768L); /* t0 = 2.0*x*b1 - b2 */
t0 = L_msu(t0, b2_l, 1);
t0 = L_mac(t0, f[i], 4096); /* t0 = 2.0*x*b1 - b2 + f[i]; */
L_Extract(t0, &b0_h, &b0_l); /* b0 = 2.0*x*b1 - b2 + f[i]; */
b2_l = b1_l; /* b2 = b1; */
b2_h = b1_h;
b1_l = b0_l; /* b1 = b0; */
b1_h = b0_h;
}
t0 = Mpy_32_16(b1_h, b1_l, x); /* t0 = x*b1; */
t0 = L_mac(t0, b2_h,(Word16)-32768L); /* t0 = x*b1 - b2 */
t0 = L_msu(t0, b2_l, 1);
t0 = L_mac(t0, f[i], 2048); /* t0 = x*b1 - b2 + f[i]/2 */
t0 = L_shl(t0, 6); /* Q24 to Q30 with saturation */
cheb = extract_h(t0); /* Result in Q14 */
return(cheb);
}
static Word16 Chebps_10(Word16 x, Word16 f[], Word16 n)
{
Word16 i, cheb;
Word16 b0_h, b0_l, b1_h, b1_l, b2_h, b2_l;
Word32 t0;
/* Note: All computation are done in Q23. */
b2_h = 128; /* b2 = 1.0 in Q23 DPF */
b2_l = 0;
t0 = L_mult(x, 256); /* 2*x in Q23 */
t0 = L_mac(t0, f[1], 4096); /* + f[1] in Q23 */
L_Extract(t0, &b1_h, &b1_l); /* b1 = 2*x + f[1] */
for (i = 2; i<n; i++)
{
t0 = Mpy_32_16(b1_h, b1_l, x); /* t0 = 2.0*x*b1 */
t0 = L_shl(t0, 1);
t0 = L_mac(t0,b2_h,(Word16)-32768L); /* t0 = 2.0*x*b1 - b2 */
t0 = L_msu(t0, b2_l, 1);
t0 = L_mac(t0, f[i], 4096); /* t0 = 2.0*x*b1 - b2 + f[i]; */
L_Extract(t0, &b0_h, &b0_l); /* b0 = 2.0*x*b1 - b2 + f[i]; */
b2_l = b1_l; /* b2 = b1; */
b2_h = b1_h;
b1_l = b0_l; /* b1 = b0; */
b1_h = b0_h;
}
t0 = Mpy_32_16(b1_h, b1_l, x); /* t0 = x*b1; */
t0 = L_mac(t0, b2_h,(Word16)-32768L); /* t0 = x*b1 - b2 */
t0 = L_msu(t0, b2_l, 1);
t0 = L_mac(t0, f[i], 2048); /* t0 = x*b1 - b2 + f[i]/2 */
t0 = L_shl(t0, 7); /* Q23 to Q30 with saturation */
cheb = extract_h(t0); /* Result in Q14 */
return(cheb);
}
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