ape: make version-dependent decoding functions called via pointers

This will help in supporting old versions, e.g. version 3.93 uses the same
range coder but different predictor and version 3.82 uses different range
coder and predictor. Also this should not make decoding newer versions slower
by introducing additional checks on versions.

libavcodec/apedec.c

@@ -161,8 +161,24 @@ typedef struct APEContext {
     const uint8_t *ptr;                      ///< current position in frame data
 
     int error;
+
+    void (*entropy_decode_mono)(struct APEContext *ctx, int blockstodecode);
+    void (*entropy_decode_stereo)(struct APEContext *ctx, int blockstodecode);
+    void (*predictor_decode_mono)(struct APEContext *ctx, int count);
+    void (*predictor_decode_stereo)(struct APEContext *ctx, int count);
 } APEContext;
 
+static void ape_apply_filters(APEContext *ctx, int32_t *decoded0,
+                              int32_t *decoded1, int count);
+
+static void entropy_decode_mono_3900(APEContext *ctx, int blockstodecode);
+static void entropy_decode_stereo_3900(APEContext *ctx, int blockstodecode);
+static void entropy_decode_mono_3990(APEContext *ctx, int blockstodecode);
+static void entropy_decode_stereo_3990(APEContext *ctx, int blockstodecode);
+
+static void predictor_decode_mono_3950(APEContext *ctx, int count);
+static void predictor_decode_stereo_3950(APEContext *ctx, int count);
+
 // TODO: dsputilize
 
 static av_cold int ape_decode_close(AVCodecContext *avctx)
@@ -231,6 +247,17 @@ static av_cold int ape_decode_init(AVCodecContext *avctx)
                          filter_alloc_fail);
     }
 
+    if (s->fileversion < 3990) {
+        s->entropy_decode_mono   = entropy_decode_mono_3900;
+        s->entropy_decode_stereo = entropy_decode_stereo_3900;
+    } else {
+        s->entropy_decode_mono   = entropy_decode_mono_3990;
+        s->entropy_decode_stereo = entropy_decode_stereo_3990;
+    }
+
+    s->predictor_decode_mono   = predictor_decode_mono_3950;
+    s->predictor_decode_stereo = predictor_decode_stereo_3950;
+
     ff_dsputil_init(&s->dsp, avctx);
     avctx->channel_layout = (avctx->channels==2) ? AV_CH_LAYOUT_STEREO : AV_CH_LAYOUT_MONO;
 
@@ -401,67 +428,76 @@ static inline void update_rice(APERice *rice, unsigned int x)
         rice->k++;
 }
 
-static inline int ape_decode_value(APEContext *ctx, APERice *rice)
+static inline int ape_decode_value_3900(APEContext *ctx, APERice *rice)
 {
     unsigned int x, overflow;
+    int tmpk;
 
-    if (ctx->fileversion < 3990) {
-        int tmpk;
+    overflow = range_get_symbol(ctx, counts_3970, counts_diff_3970);
 
-        overflow = range_get_symbol(ctx, counts_3970, counts_diff_3970);
+    if (overflow == (MODEL_ELEMENTS - 1)) {
+        tmpk = range_decode_bits(ctx, 5);
+        overflow = 0;
+    } else
+        tmpk = (rice->k < 1) ? 0 : rice->k - 1;
 
-        if (overflow == (MODEL_ELEMENTS - 1)) {
-            tmpk = range_decode_bits(ctx, 5);
-            overflow = 0;
-        } else
-            tmpk = (rice->k < 1) ? 0 : rice->k - 1;
-
-        if (tmpk <= 16)
-            x = range_decode_bits(ctx, tmpk);
-        else if (tmpk <= 32) {
-            x = range_decode_bits(ctx, 16);
-            x |= (range_decode_bits(ctx, tmpk - 16) << 16);
-        } else {
-            av_log(ctx->avctx, AV_LOG_ERROR, "Too many bits: %d\n", tmpk);
-            return AVERROR_INVALIDDATA;
-        }
-        x += overflow << tmpk;
+    if (tmpk <= 16)
+        x = range_decode_bits(ctx, tmpk);
+    else if (tmpk <= 32) {
+        x = range_decode_bits(ctx, 16);
+        x |= (range_decode_bits(ctx, tmpk - 16) << 16);
     } else {
-        int base, pivot;
+        av_log(ctx->avctx, AV_LOG_ERROR, "Too many bits: %d\n", tmpk);
+        return AVERROR_INVALIDDATA;
+    }
+    x += overflow << tmpk;
+
+    update_rice(rice, x);
+
+    /* Convert to signed */
+    if (x & 1)
+        return (x >> 1) + 1;
+    else
+        return -(x >> 1);
+}
 
-        pivot = rice->ksum >> 5;
-        if (pivot == 0)
-            pivot = 1;
+static inline int ape_decode_value_3990(APEContext *ctx, APERice *rice)
+{
+    unsigned int x, overflow;
+    int base, pivot;
 
-        overflow = range_get_symbol(ctx, counts_3980, counts_diff_3980);
+    pivot = rice->ksum >> 5;
+    if (pivot == 0)
+        pivot = 1;
 
-        if (overflow == (MODEL_ELEMENTS - 1)) {
-            overflow  = range_decode_bits(ctx, 16) << 16;
-            overflow |= range_decode_bits(ctx, 16);
-        }
+    overflow = range_get_symbol(ctx, counts_3980, counts_diff_3980);
 
-        if (pivot < 0x10000) {
-            base = range_decode_culfreq(ctx, pivot);
-            range_decode_update(ctx, 1, base);
-        } else {
-            int base_hi = pivot, base_lo;
-            int bbits = 0;
-
-            while (base_hi & ~0xFFFF) {
-                base_hi >>= 1;
-                bbits++;
-            }
-            base_hi = range_decode_culfreq(ctx, base_hi + 1);
-            range_decode_update(ctx, 1, base_hi);
-            base_lo = range_decode_culfreq(ctx, 1 << bbits);
-            range_decode_update(ctx, 1, base_lo);
-
-            base = (base_hi << bbits) + base_lo;
+    if (overflow == (MODEL_ELEMENTS - 1)) {
+        overflow  = range_decode_bits(ctx, 16) << 16;
+        overflow |= range_decode_bits(ctx, 16);
+    }
+
+    if (pivot < 0x10000) {
+        base = range_decode_culfreq(ctx, pivot);
+        range_decode_update(ctx, 1, base);
+    } else {
+        int base_hi = pivot, base_lo;
+        int bbits = 0;
+
+        while (base_hi & ~0xFFFF) {
+            base_hi >>= 1;
+            bbits++;
         }
+        base_hi = range_decode_culfreq(ctx, base_hi + 1);
+        range_decode_update(ctx, 1, base_hi);
+        base_lo = range_decode_culfreq(ctx, 1 << bbits);
+        range_decode_update(ctx, 1, base_lo);
 
-        x = base + overflow * pivot;
+        base = (base_hi << bbits) + base_lo;
     }
 
+    x = base + overflow * pivot;
+
     update_rice(rice, x);
 
     /* Convert to signed */
@@ -471,15 +507,41 @@ static inline int ape_decode_value(APEContext *ctx, APERice *rice)
         return -(x >> 1);
 }
 
-static void entropy_decode(APEContext *ctx, int blockstodecode, int stereo)
+static void entropy_decode_mono_3900(APEContext *ctx, int blockstodecode)
+{
+    int32_t *decoded0 = ctx->decoded[0];
+
+    while (blockstodecode--)
+        *decoded0++ = ape_decode_value_3900(ctx, &ctx->riceY);
+}
+
+static void entropy_decode_stereo_3900(APEContext *ctx, int blockstodecode)
 {
     int32_t *decoded0 = ctx->decoded[0];
     int32_t *decoded1 = ctx->decoded[1];
 
     while (blockstodecode--) {
-        *decoded0++ = ape_decode_value(ctx, &ctx->riceY);
-        if (stereo)
-            *decoded1++ = ape_decode_value(ctx, &ctx->riceX);
+        *decoded0++ = ape_decode_value_3900(ctx, &ctx->riceY);
+        *decoded1++ = ape_decode_value_3900(ctx, &ctx->riceX);
+    }
+}
+
+static void entropy_decode_mono_3990(APEContext *ctx, int blockstodecode)
+{
+    int32_t *decoded0 = ctx->decoded[0];
+
+    while (blockstodecode--)
+        *decoded0++ = ape_decode_value_3990(ctx, &ctx->riceY);
+}
+
+static void entropy_decode_stereo_3990(APEContext *ctx, int blockstodecode)
+{
+    int32_t *decoded0 = ctx->decoded[0];
+    int32_t *decoded1 = ctx->decoded[1];
+
+    while (blockstodecode--) {
+        *decoded0++ = ape_decode_value_3990(ctx, &ctx->riceY);
+        *decoded1++ = ape_decode_value_3990(ctx, &ctx->riceX);
     }
 }
 
@@ -588,12 +650,14 @@ static av_always_inline int predictor_update_filter(APEPredictor *p,
     return p->filterA[filter];
 }
 
-static void predictor_decode_stereo(APEContext *ctx, int count)
+static void predictor_decode_stereo_3950(APEContext *ctx, int count)
 {
     APEPredictor *p = &ctx->predictor;
     int32_t *decoded0 = ctx->decoded[0];
     int32_t *decoded1 = ctx->decoded[1];
 
+    ape_apply_filters(ctx, ctx->decoded[0], ctx->decoded[1], count);
+
     while (count--) {
         /* Predictor Y */
         *decoded0 = predictor_update_filter(p, *decoded0, 0, YDELAYA, YDELAYB,
@@ -615,12 +679,14 @@ static void predictor_decode_stereo(APEContext *ctx, int count)
     }
 }
 
-static void predictor_decode_mono(APEContext *ctx, int count)
+static void predictor_decode_mono_3950(APEContext *ctx, int count)
 {
     APEPredictor *p = &ctx->predictor;
     int32_t *decoded0 = ctx->decoded[0];
     int32_t predictionA, currentA, A, sign;
 
+    ape_apply_filters(ctx, ctx->decoded[0], NULL, count);
+
     currentA = p->lastA[0];
 
     while (count--) {
@@ -779,11 +845,10 @@ static void ape_unpack_mono(APEContext *ctx, int count)
         return;
     }
 
-    entropy_decode(ctx, count, 0);
-    ape_apply_filters(ctx, ctx->decoded[0], NULL, count);
+    ctx->entropy_decode_mono(ctx, count);
 
     /* Now apply the predictor decoding */
-    predictor_decode_mono(ctx, count);
+    ctx->predictor_decode_mono(ctx, count);
 
     /* Pseudo-stereo - just copy left channel to right channel */
     if (ctx->channels == 2) {
@@ -803,11 +868,10 @@ static void ape_unpack_stereo(APEContext *ctx, int count)
         return;
     }
 
-    entropy_decode(ctx, count, 1);
-    ape_apply_filters(ctx, decoded0, decoded1, count);
+    ctx->entropy_decode_stereo(ctx, count);
 
     /* Now apply the predictor decoding */
-    predictor_decode_stereo(ctx, count);
+    ctx->predictor_decode_stereo(ctx, count);
 
     /* Decorrelate and scale to output depth */
     while (count--) {