split ac3_parametric_bit_allocation into 3 separate functions

Originally committed as revision 8442 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3.c

@@ -50,20 +50,10 @@ static inline int calc_lowcomp(int a, int b0, int b1, int bin)
     }
 }
 
-/* AC3 bit allocation. The algorithm is the one described in the AC3
-   spec. */
-void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
-                                   int8_t *exp, int start, int end,
-                                   int snroffset, int fgain, int is_lfe,
-                                   int deltbae,int deltnseg,
-                                   uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)
+void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
+                               int16_t *bndpsd)
 {
-    int bin,i,j,k,end1,v,bndstrt,bndend,lowcomp,begin;
-    int fastleak,slowleak,address,tmp;
-    int16_t psd[256]; /* scaled exponents */
-    int16_t bndpsd[50]; /* interpolated exponents */
-    int16_t excite[50]; /* excitation */
-    int16_t mask[50];   /* masking value */
+    int bin, i, j, k, end1, v;
 
     /* exponent mapping to PSD */
     for(bin=start;bin<end;bin++) {
@@ -86,6 +76,18 @@ void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
         bndpsd[k]=v;
         k++;
     } while (end > bndtab[k]);
+}
+
+void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
+                                int start, int end, int fgain, int is_lfe,
+                                int deltbae, int deltnseg, uint8_t *deltoffst,
+                                uint8_t *deltlen, uint8_t *deltba,
+                                int16_t *mask)
+{
+    int16_t excite[50]; /* excitation */
+    int bin, k;
+    int bndstrt, bndend, begin, end1, tmp;
+    int lowcomp, fastleak, slowleak;
 
     /* excitation function */
     bndstrt = masktab[start];
@@ -166,13 +168,17 @@ void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
             }
         }
     }
+}
 
-    /* compute bit allocation */
+void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
+                               int snroffset, int floor, uint8_t *bap)
+{
+    int i, j, k, end1, v, address;
 
     i = start;
     j = masktab[start];
     do {
-        v = (FFMAX(mask[j] - snroffset - s->floor, 0) & 0x1FE0) + s->floor;
+        v = (FFMAX(mask[j] - snroffset - floor, 0) & 0x1FE0) + floor;
         end1 = FFMIN(bndtab[j] + bndsz[j], end);
         for (k = i; k < end1; k++) {
             address = av_clip((psd[i] - v) >> 5, 0, 63);
@@ -182,6 +188,28 @@ void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
     } while (end > bndtab[j++]);
 }
 
+/* AC3 bit allocation. The algorithm is the one described in the AC3
+   spec. */
+void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
+                                   int8_t *exp, int start, int end,
+                                   int snroffset, int fgain, int is_lfe,
+                                   int deltbae,int deltnseg,
+                                   uint8_t *deltoffst, uint8_t *deltlen,
+                                   uint8_t *deltba)
+{
+    int16_t psd[256];   /* scaled exponents */
+    int16_t bndpsd[50]; /* interpolated exponents */
+    int16_t mask[50];   /* masking value */
+
+    ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, bndpsd);
+
+    ff_ac3_bit_alloc_calc_mask(s, bndpsd, start, end, fgain, is_lfe,
+                               deltbae, deltnseg, deltoffst, deltlen, deltba,
+                               mask);
+
+    ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snroffset, s->floor, bap);
+}
+
 /**
  * Initializes some tables.
  * note: This function must remain thread safe because it is called by the

libavcodec/ac3.h

@@ -102,6 +102,68 @@ extern const int16_t ff_floortab[8];
 extern const uint16_t ff_fgaintab[8];
 
 void ac3_common_init(void);
+
+/**
+ * Calculates the log power-spectral density of the input signal.
+ * This gives a rough estimate of signal power in the frequency domain by using
+ * the spectral envelope (exponents).  The psd is also separately grouped
+ * into critical bands for use in the calculating the masking curve.
+ * 128 units in psd = -6 dB.  The dbknee parameter in AC3BitAllocParameters
+ * determines the reference level.
+ *
+ * @param[in]  exp        frequency coefficient exponents
+ * @param[in]  start      starting bin location
+ * @param[in]  end        ending bin location
+ * @param[out] psd        signal power for each frequency bin
+ * @param[out] bndpsd     signal power for each critical band
+ */
+void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd,
+                               int16_t *bndpsd);
+
+/**
+ * Calculates the masking curve.
+ * First, the excitation is calculated using parameters in \p s and the signal
+ * power in each critical band.  The excitation is compared with a predefined
+ * hearing threshold table to produce the masking curve.  If delta bit
+ * allocation information is provided, it is used for adjusting the masking
+ * curve, usually to give a closer match to a better psychoacoustic model.
+ *
+ * @param[in]  s          adjustable bit allocation parameters
+ * @param[in]  bndpsd     signal power for each critical band
+ * @param[in]  start      starting bin location
+ * @param[in]  end        ending bin location
+ * @param[in]  fgain      fast gain (estimated signal-to-mask ratio)
+ * @param[in]  is_lfe     whether or not the channel being processed is the LFE
+ * @param[in]  deltbae    delta bit allocation exists (none, reuse, or new)
+ * @param[in]  deltnseg   number of delta segments
+ * @param[in]  deltoffst  location offsets for each segment
+ * @param[in]  deltlen    length of each segment
+ * @param[in]  deltba     delta bit allocation for each segment
+ * @param[out] mask       calculated masking curve
+ */
+void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd,
+                                int start, int end, int fgain, int is_lfe,
+                                int deltbae, int deltnseg, uint8_t *deltoffst,
+                                uint8_t *deltlen, uint8_t *deltba,
+                                int16_t *mask);
+
+/**
+ * Calculates bit allocation pointers.
+ * The SNR is the difference between the masking curve and the signal.  AC-3
+ * uses this value for each frequency bin to allocate bits.  The \p snroffset
+ * parameter is a global adjustment to the SNR for all bins.
+ *
+ * @param[in]  mask       masking curve
+ * @param[in]  psd        signal power for each frequency bin
+ * @param[in]  start      starting bin location
+ * @param[in]  end        ending bin location
+ * @param[in]  snroffset  SNR adjustment
+ * @param[in]  floor      noise floor
+ * @param[out] bap        bit allocation pointers
+ */
+void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end,
+                               int snroffset, int floor, uint8_t *bap);
+
 void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
                                    int8_t *exp, int start, int end,
                                    int snroffset, int fgain, int is_lfe,