Use 24-bit fixed-point transform coefficients until just before MDCT. This

gives 7% faster decoding on average.

Originally committed as revision 12284 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -45,22 +45,16 @@
  */
 static const uint8_t rematrix_band_tab[5] = { 13, 25, 37, 61, 253 };
 
-/**
- * table for exponent to scale_factor mapping
- * scale_factors[i] = 2 ^ -i
- */
-static float scale_factors[25];
-
 /** table for grouping exponents */
 static uint8_t exp_ungroup_tab[128][3];
 
 
 /** tables for ungrouping mantissas */
-static float b1_mantissas[32][3];
-static float b2_mantissas[128][3];
-static float b3_mantissas[8];
-static float b4_mantissas[128][2];
-static float b5_mantissas[16];
+static int b1_mantissas[32][3];
+static int b2_mantissas[128][3];
+static int b3_mantissas[8];
+static int b4_mantissas[128][2];
+static int b5_mantissas[16];
 
 /**
  * Quantization table: levels for symmetric. bits for asymmetric.
@@ -161,7 +155,7 @@ typedef struct {
     int surround_mix_level;                 ///< Surround mix level index
     float downmix_coeffs[AC3_MAX_CHANNELS][2];  ///< stereo downmix coefficients
     float dynamic_range[2];                 ///< dynamic range
-    float cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates
+    int   cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates
     int   num_cpl_bands;                    ///< number of coupling bands
     int   num_cpl_subbands;                 ///< number of coupling sub bands
     int   start_freq[AC3_MAX_CHANNELS];     ///< start frequency bin
@@ -174,6 +168,7 @@ typedef struct {
     int16_t band_psd[AC3_MAX_CHANNELS][50]; ///< interpolated exponents
     int16_t mask[AC3_MAX_CHANNELS][50];     ///< masking curve values
 
+    int fixed_coeffs[AC3_MAX_CHANNELS][256];    ///> fixed-point transform coefficients
     DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]);  ///< transform coefficients
 
     /* For IMDCT. */
@@ -201,10 +196,10 @@ typedef struct {
  * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
  *            Tables 7.19 to 7.23
  */
-static inline float
+static inline int
 symmetric_dequant(int code, int levels)
 {
-    return (code - (levels >> 1)) * (2.0f / levels);
+    return ((code - (levels >> 1)) << 24) / levels;
 }
 
 /*
@@ -250,11 +245,6 @@ static void ac3_tables_init(void)
         dynamic_range_tab[i] = powf(2.0f, v) * ((i & 0x1F) | 0x20);
     }
 
-    /* generate scale factors for exponents and asymmetrical dequantization
-       reference: Section 7.3.2 Expansion of Mantissas for Asymmetric Quantization */
-    for (i = 0; i < 25; i++)
-        scale_factors[i] = pow(2.0, -i);
-
     /* generate exponent tables
        reference: Section 7.1.3 Exponent Decoding */
     for(i=0; i<128; i++) {
@@ -461,9 +451,9 @@ static void uncouple_channels(AC3DecodeContext *s)
             for(j=0; j<12; j++) {
                 for(ch=1; ch<=s->fbw_channels; ch++) {
                     if(s->channel_in_cpl[ch]) {
-                        s->transform_coeffs[ch][i] = s->transform_coeffs[CPL_CH][i] * s->cpl_coords[ch][bnd] * 8.0f;
+                        s->fixed_coeffs[ch][i] = ((int64_t)s->fixed_coeffs[CPL_CH][i] * (int64_t)s->cpl_coords[ch][bnd]) >> 23;
                         if (ch == 2 && s->phase_flags[bnd])
-                            s->transform_coeffs[ch][i] = -s->transform_coeffs[ch][i];
+                            s->fixed_coeffs[ch][i] = -s->fixed_coeffs[ch][i];
                     }
                 }
                 i++;
@@ -476,9 +466,9 @@ static void uncouple_channels(AC3DecodeContext *s)
  * Grouped mantissas for 3-level 5-level and 11-level quantization
  */
 typedef struct {
-    float b1_mant[3];
-    float b2_mant[3];
-    float b4_mant[2];
+    int b1_mant[3];
+    int b2_mant[3];
+    int b4_mant[2];
     int b1ptr;
     int b2ptr;
     int b4ptr;
@@ -494,11 +484,11 @@ static int get_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_group
     int i, gcode, tbap, start, end;
     uint8_t *exps;
     uint8_t *bap;
-    float *coeffs;
+    int *coeffs;
 
     exps = s->dexps[ch_index];
     bap = s->bap[ch_index];
-    coeffs = s->transform_coeffs[ch_index];
+    coeffs = s->fixed_coeffs[ch_index];
     start = s->start_freq[ch_index];
     end = s->end_freq[ch_index];
 
@@ -506,7 +496,7 @@ static int get_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_group
         tbap = bap[i];
         switch (tbap) {
             case 0:
-                coeffs[i] = ((av_random(&s->dith_state) & 0xFFFF) / 65535.0f) - 0.5f;
+                coeffs[i] = (av_random(&s->dith_state) & 0x7FFFFF) - 4194304;
                 break;
 
             case 1:
@@ -549,12 +539,14 @@ static int get_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_group
                 coeffs[i] = b5_mantissas[get_bits(gbc, 4)];
                 break;
 
-            default:
+            default: {
                 /* asymmetric dequantization */
-                coeffs[i] = get_sbits(gbc, quantization_tab[tbap]) * scale_factors[quantization_tab[tbap]-1];
+                int qlevel = quantization_tab[tbap];
+                coeffs[i] = get_sbits(gbc, qlevel) << (24 - qlevel);
                 break;
             }
-        coeffs[i] *= scale_factors[exps[i]];
+        }
+        coeffs[i] >>= exps[i];
     }
 
     return 0;
@@ -567,12 +559,12 @@ static int get_transform_coeffs_ch(AC3DecodeContext *s, int ch_index, mant_group
 static void remove_dithering(AC3DecodeContext *s) {
     int ch, i;
     int end=0;
-    float *coeffs;
+    int *coeffs;
     uint8_t *bap;
 
     for(ch=1; ch<=s->fbw_channels; ch++) {
         if(!s->dither_flag[ch]) {
-            coeffs = s->transform_coeffs[ch];
+            coeffs = s->fixed_coeffs[ch];
             bap = s->bap[ch];
             if(s->channel_in_cpl[ch])
                 end = s->start_freq[CPL_CH];
@@ -580,13 +572,13 @@ static void remove_dithering(AC3DecodeContext *s) {
                 end = s->end_freq[ch];
             for(i=0; i<end; i++) {
                 if(!bap[i])
-                    coeffs[i] = 0.0f;
+                    coeffs[i] = 0;
             }
             if(s->channel_in_cpl[ch]) {
                 bap = s->bap[CPL_CH];
                 for(; i<s->end_freq[CPL_CH]; i++) {
                     if(!bap[i])
-                        coeffs[i] = 0.0f;
+                        coeffs[i] = 0;
                 }
             }
         }
@@ -643,7 +635,7 @@ static void do_rematrixing(AC3DecodeContext *s)
 {
     int bnd, i;
     int end, bndend;
-    float tmp0, tmp1;
+    int tmp0, tmp1;
 
     end = FFMIN(s->end_freq[1], s->end_freq[2]);
 
@@ -651,10 +643,10 @@ static void do_rematrixing(AC3DecodeContext *s)
         if(s->rematrixing_flags[bnd]) {
             bndend = FFMIN(end, rematrix_band_tab[bnd+1]);
             for(i=rematrix_band_tab[bnd]; i<bndend; i++) {
-                tmp0 = s->transform_coeffs[1][i];
-                tmp1 = s->transform_coeffs[2][i];
-                s->transform_coeffs[1][i] = tmp0 + tmp1;
-                s->transform_coeffs[2][i] = tmp0 - tmp1;
+                tmp0 = s->fixed_coeffs[1][i];
+                tmp1 = s->fixed_coeffs[2][i];
+                s->fixed_coeffs[1][i] = tmp0 + tmp1;
+                s->fixed_coeffs[2][i] = tmp0 - tmp1;
             }
         }
     }
@@ -851,10 +843,10 @@ static int ac3_parse_audio_block(AC3DecodeContext *s, int blk)
                         cpl_coord_exp = get_bits(gbc, 4);
                         cpl_coord_mant = get_bits(gbc, 4);
                         if (cpl_coord_exp == 15)
-                            s->cpl_coords[ch][bnd] = cpl_coord_mant / 16.0f;
+                            s->cpl_coords[ch][bnd] = cpl_coord_mant << 22;
                         else
-                            s->cpl_coords[ch][bnd] = (cpl_coord_mant + 16.0f) / 32.0f;
-                        s->cpl_coords[ch][bnd] *= scale_factors[cpl_coord_exp + master_cpl_coord];
+                            s->cpl_coords[ch][bnd] = (cpl_coord_mant + 16) << 21;
+                        s->cpl_coords[ch][bnd] >>= (cpl_coord_exp + master_cpl_coord);
                     }
                 }
             }
@@ -1037,14 +1029,14 @@ static int ac3_parse_audio_block(AC3DecodeContext *s, int blk)
 
     /* apply scaling to coefficients (headroom, dynrng) */
     for(ch=1; ch<=s->channels; ch++) {
-        float gain = 2.0f * s->mul_bias;
+        float gain = s->mul_bias / 4194304.0f;
         if(s->channel_mode == AC3_CHMODE_DUALMONO) {
             gain *= s->dynamic_range[ch-1];
         } else {
             gain *= s->dynamic_range[0];
         }
-        for(i=0; i<s->end_freq[ch]; i++) {
-            s->transform_coeffs[ch][i] *= gain;
+        for(i=0; i<256; i++) {
+            s->transform_coeffs[ch][i] = s->fixed_coeffs[ch][i] * gain;
         }
     }