ref: dc68eb231f98533b61d5451233a1d518729946cf
parent: feca095e96ecadb810f50145d67bf84aa8d1246c
author: Jean-Marc Valin <[email protected]>
date: Sat Jun 19 06:27:28 EDT 2010
Comments, code cleanup
--- a/libcelt/bands.c
+++ b/libcelt/bands.c
@@ -553,6 +553,8 @@
spread0 = spread;
N_B0 = N_B;
}
+
+ /* Reorganize the samples in time order instead of frequency order */
if (!stereo && spread0>1 && level==0)
{if (encode)
@@ -583,6 +585,8 @@
celt_word16 mid, side;
int offset, N2;
offset = m->logN[i]+(LM<<BITRES)-QTHETA_OFFSET;
+
+ /* Decide on the resolution to give to the split parameter theta */
N2 = 2*N-1;
if (stereo && N>2)
N2--;
@@ -609,8 +613,12 @@
mid = renormalise_vector(X, Q15ONE, N, 1);
side = renormalise_vector(Y, Q15ONE, N, 1);
- /* 0.63662 = 2/pi */
+ /* theta is the atan() of the ration between the (normalized)
+ side and mid. With just that parameter, we can re-scale both
+ mid and side because we know that 1) they have unit norm and
+ 2) they are orthogonal. */
#ifdef FIXED_POINT
+ /* 0.63662 = 2/pi */
itheta = MULT16_16_Q15(QCONST16(0.63662f,15),celt_atan2p(side, mid));
#else
itheta = floor(.5f+16384*0.63662f*atan2(side,mid));
@@ -685,6 +693,8 @@
} else {imid = bitexact_cos(itheta);
iside = bitexact_cos(16384-itheta);
+ /* This is the mid vs side allocation that minimizes squared error
+ in that band. */
delta = (N-1)*(log2_frac(iside,BITRES+2)-log2_frac(imid,BITRES+2))>>2;
}
@@ -806,6 +816,7 @@
alg_unquant(X, N, q, spread, lowband, (ec_dec*)ec);
}
+ /* This code is used by the decoder and by the resynthesis-enabled encoder */
if (resynth)
{int k;
@@ -834,6 +845,7 @@
interleave_vector(lowband, N_B, spread0);
}
+ /* Undo time-freq changes that we did earlier */
N_B = N_B0;
spread = spread0;
for (k=0;k<time_divide;k++)
@@ -931,12 +943,6 @@
} else
lowband = NULL;
- /*if (shortBlocks)
- {- tf_change = tf_res[i] ? -1 : 2;
- } else {- tf_change = tf_res[i] ? -2 : 0;
- }*/
tf_change = tf_res[i];
quant_band(encode, m, i, X, Y, N, b, spread, tf_change, lowband, resynth, ec, &remaining_bits, LM, norm+M*eBands[i], bandE, 0);
--- a/libcelt/mathops.h
+++ b/libcelt/mathops.h
@@ -76,7 +76,11 @@
}
#endif
+/* Multiplies two 16-bit fractional values. Bit-exactness of this macro is important */
#define FRAC_MUL16(a,b) ((16384+((celt_int32)(celt_int16)(a)*(celt_int16)(b)))>>15)
+
+/* This is a cos() approximation designed to be bit-exact on any platform. Bit exactness
+ with this approximation is important because it has an impact on the bit allocation */
static inline celt_int16 bitexact_cos(celt_int16 x)
{celt_int32 tmp;
@@ -231,7 +235,7 @@
int k;
celt_word16 n;
celt_word32 rt;
- const celt_word16 C[5] = {23175, 11561, -3011, 1699, -664};+ static const celt_word16 C[5] = {23175, 11561, -3011, 1699, -664};if (x==0)
return 0;
k = (celt_ilog2(x)>>1)-7;
@@ -250,7 +254,7 @@
int k;
celt_word16 n;
celt_word32 rt;
- const celt_word16 C[5] = {23175, 11561, -3011, 1699, -664};+ static const celt_word16 C[5] = {23175, 11561, -3011, 1699, -664};k = (celt_ilog2(x)>>1)-7;
x = VSHR32(x, (k<<1));
n = x-32768;
@@ -308,7 +312,7 @@
celt_word16 n, frac;
/* -0.41509302963303146, 0.9609890551383969, -0.31836011537636605,
0.15530808010959576, -0.08556153059057618 */
- const celt_word16 C[5] = {-6801+(1<<13-DB_SHIFT), 15746, -5217, 2545, -1401};+ static const celt_word16 C[5] = {-6801+(1<<13-DB_SHIFT), 15746, -5217, 2545, -1401};if (x==0)
return -32767;
i = celt_ilog2(x);
@@ -379,6 +383,8 @@
#define M3 -11943
#define M4 4936
+/* Atan approximation using a 4th order polynomial. Input is in Q15 format
+ and normalized by pi/4. Output is in Q15 format */
static inline celt_word16 celt_atan01(celt_word16 x)
{return MULT16_16_P15(x, ADD32(M1, MULT16_16_P15(x, ADD32(M2, MULT16_16_P15(x, ADD32(M3, MULT16_16_P15(M4, x)))))));
@@ -389,6 +395,7 @@
#undef M3
#undef M4
+/* atan2() approximation valid for positive input values */
static inline celt_word16 celt_atan2p(celt_word16 y, celt_word16 x)
{if (y < x)