atrac3: Generalize gain compensation code

Move it to the ATRAC common code, so it can be reused
in the umpcoming ATRAC3+ decoder.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/atrac.c

@@ -63,6 +63,67 @@ av_cold void ff_atrac_generate_tables(void)
         }
 }
 
+av_cold void ff_atrac_init_gain_compensation(AtracGCContext *gctx, int id2exp_offset,
+                                             int loc_scale)
+{
+    int i;
+
+    gctx->loc_scale     = loc_scale;
+    gctx->loc_size      = 1 << loc_scale;
+    gctx->id2exp_offset = id2exp_offset;
+
+    /* Generate gain level table. */
+    for (i = 0; i < 16; i++)
+        gctx->gain_tab1[i] = powf(2.0, id2exp_offset - i);
+
+    /* Generate gain interpolation table. */
+    for (i = -15; i < 16; i++)
+        gctx->gain_tab2[i + 15] = powf(2.0, -1.0f / gctx->loc_size * i);
+}
+
+void ff_atrac_gain_compensation(AtracGCContext *gctx, float *in, float *prev,
+                                AtracGainInfo *gc_now, AtracGainInfo *gc_next,
+                                int num_samples, float *out)
+{
+    float lev, gc_scale, gain_inc;
+    int i, pos, lastpos;
+
+    gc_scale = gc_next->num_points ? gctx->gain_tab1[gc_next->levcode[0]] : 1.0f;
+
+    if (!gc_now->num_points) {
+        for (pos = 0; pos < num_samples; pos++)
+            out[pos] = in[pos] * gc_scale + prev[pos];
+    } else {
+        pos = 0;
+
+        for (i = 0; i < gc_now->num_points; i++) {
+            lastpos = gc_now->loccode[i] << gctx->loc_scale;
+
+            lev = gctx->gain_tab1[gc_now->levcode[i]];
+            gain_inc = gctx->gain_tab2[(i + 1 < gc_now->num_points
+                                       ? gc_now->levcode[i + 1]
+                                       : gctx->id2exp_offset)
+                                       - gc_now->levcode[i] + 15];
+
+            /* apply constant gain level and overlap */
+            for (; pos < lastpos; pos++)
+                out[pos] = (in[pos] * gc_scale + prev[pos]) * lev;
+
+            /* interpolate between two different gain levels */
+            for (; pos < lastpos + gctx->loc_size; pos++) {
+                out[pos] = (in[pos] * gc_scale + prev[pos]) * lev;
+                lev *= gain_inc;
+            }
+        }
+
+        for (; pos < num_samples; pos++)
+            out[pos] = in[pos] * gc_scale + prev[pos];
+    }
+
+    /* copy the overlapping part into the delay buffer */
+    memcpy(prev, &in[num_samples], num_samples * sizeof(float));
+}
+
 void ff_atrac_iqmf(float *inlo, float *inhi, unsigned int nIn, float *pOut,
                    float *delayBuf, float *temp)
 {

libavcodec/atrac.h

@@ -29,6 +29,26 @@
 #ifndef AVCODEC_ATRAC_H
 #define AVCODEC_ATRAC_H
 
+/**
+ *  Gain control parameters for one subband.
+ */
+typedef struct AtracGainInfo {
+    int   num_points; ///< number of gain control points
+    int   levcode[7]; ///< level at corresponding control point
+    int   loccode[7]; ///< location of gain control points
+} AtracGainInfo;
+
+/**
+ *  Gain compensation context structure.
+ */
+typedef struct AtracGCContext {
+    float   gain_tab1[16]; ///< gain compensation level table
+    float   gain_tab2[31]; ///< gain compensation interpolation table
+    int     id2exp_offset; ///< offset for converting level index into level exponent
+    int     loc_scale;     ///< scale of location code = 2^loc_scale samples
+    int     loc_size;      ///< size of location code in samples
+} AtracGCContext;
+
 extern float ff_atrac_sf_table[64];
 
 /**
@@ -36,6 +56,31 @@ extern float ff_atrac_sf_table[64];
  */
 void ff_atrac_generate_tables(void);
 
+/**
+ *  Initialize gain compensation context.
+ *
+ * @param gctx            pointer to gain compensation context to initialize
+ * @param id2exp_offset   offset for converting level index into level exponent
+ * @param loc_scale       location size factor
+ */
+void ff_atrac_init_gain_compensation(AtracGCContext *gctx, int id2exp_offset,
+                                     int loc_scale);
+
+/**
+ * Apply gain compensation and perform the MDCT overlapping part.
+ *
+ * @param gctx         pointer to gain compensation context
+ * @param in           input buffer
+ * @param prev         previous buffer to perform overlap against
+ * @param gc_now       gain control information for current frame
+ * @param gc_next      gain control information for next frame
+ * @param num_samples  number of samples to process
+ * @param out          output data goes here
+ */
+void ff_atrac_gain_compensation(AtracGCContext *gctx, float *in, float *prev,
+                                AtracGainInfo *gc_now, AtracGainInfo *gc_next,
+                                int num_samples, float *out);
+
 /**
  * Quadrature mirror synthesis filter.
  *

libavcodec/atrac3.c

@@ -55,12 +55,6 @@
 #define SAMPLES_PER_FRAME 1024
 #define MDCT_SIZE          512
 
-typedef struct AtracGainInfo {
-    int num_points;
-    int lev_code[8];
-    int loc_code[8];
-} AtracGainInfo;
-
 typedef struct GainBlock {
     AtracGainInfo g_block[4];
 } GainBlock;
@@ -112,7 +106,8 @@ typedef struct ATRAC3Context {
     int scrambled_stream;
     //@}
 
-    FFTContext mdct_ctx;
+    AtracGCContext    gainc_ctx;
+    FFTContext        mdct_ctx;
     FmtConvertContext fmt_conv;
     AVFloatDSPContext fdsp;
 } ATRAC3Context;
@@ -443,63 +438,6 @@ static int decode_gain_control(GetBitContext *gb, GainBlock *block,
     return 0;
 }
 
-/**
- * Apply gain parameters and perform the MDCT overlapping part
- *
- * @param input   input buffer
- * @param prev    previous buffer to perform overlap against
- * @param output  output buffer
- * @param gain1   current band gain info
- * @param gain2   next band gain info
- */
-static void gain_compensate_and_overlap(float *input, float *prev,
-                                        float *output, AtracGainInfo *gain1,
-                                        AtracGainInfo *gain2)
-{
-    float g1, g2, gain_inc;
-    int i, j, num_data, start_loc, end_loc;
-
-
-    if (gain2->num_points == 0)
-        g1 = 1.0;
-    else
-        g1 = gain_tab1[gain2->lev_code[0]];
-
-    if (gain1->num_points == 0) {
-        for (i = 0; i < 256; i++)
-            output[i] = input[i] * g1 + prev[i];
-    } else {
-        num_data = gain1->num_points;
-        gain1->loc_code[num_data] = 32;
-        gain1->lev_code[num_data] = 4;
-
-        for (i = 0, j = 0; i < num_data; i++) {
-            start_loc = gain1->loc_code[i] * 8;
-            end_loc   = start_loc + 8;
-
-            g2       = gain_tab1[gain1->lev_code[i]];
-            gain_inc = gain_tab2[gain1->lev_code[i + 1] -
-                                 gain1->lev_code[i    ] + 15];
-
-            /* interpolate */
-            for (; j < start_loc; j++)
-                output[j] = (input[j] * g1 + prev[j]) * g2;
-
-            /* interpolation is done over eight samples */
-            for (; j < end_loc; j++) {
-                output[j] = (input[j] * g1 + prev[j]) * g2;
-                g2 *= gain_inc;
-            }
-        }
-
-        for (; j < 256; j++)
-            output[j] = input[j] * g1 + prev[j];
-    }
-
-    /* Delay for the overlapping part. */
-    memcpy(prev, &input[256], 256 * sizeof(*prev));
-}
-
 /**
  * Combine the tonal band spectrum and regular band spectrum
  *
@@ -690,11 +628,10 @@ static int decode_channel_sound_unit(ATRAC3Context *q, GetBitContext *gb,
             memset(snd->imdct_buf, 0, 512 * sizeof(*snd->imdct_buf));
 
         /* gain compensation and overlapping */
-        gain_compensate_and_overlap(snd->imdct_buf,
-                                    &snd->prev_frame[band * 256],
-                                    &output[band * 256],
-                                    &gain1->g_block[band],
-                                    &gain2->g_block[band]);
+        ff_atrac_gain_compensation(&q->gainc_ctx, snd->imdct_buf,
+                                   &snd->prev_frame[band * 256],
+                                   &gain1->g_block[band], &gain2->g_block[band],
+                                   256, &output[band * 256]);
     }
 
     /* Swap the gain control buffers for the next frame. */
@@ -987,6 +924,7 @@ static av_cold int atrac3_decode_init(AVCodecContext *avctx)
         q->matrix_coeff_index_next[i] = 3;
     }
 
+    ff_atrac_init_gain_compensation(&q->gainc_ctx, 4, 3);
     avpriv_float_dsp_init(&q->fdsp, avctx->flags & CODEC_FLAG_BITEXACT);
     ff_fmt_convert_init(&q->fmt_conv, avctx);