dirac: add more parse codes from the specifications

[ffmpeg] / libavcodec / cook.c

diff --git a/libavcodec/cook.c b/libavcodec/cook.c
index d8fb7368281306cb87f8b05a256b3e633cab093e..1b38019a693eb72363e78c0cfb6664c3b06de00d 100644 (file)
--- a/libavcodec/cook.c
+++ b/libavcodec/cook.c
@@ -166,10 +166,17 @@ static float rootpow2tab[127];
 /* table generator */
 static av_cold void init_pow2table(void)
 {
+    /* fast way of computing 2^i and 2^(0.5*i) for -63 <= i < 64 */
     int i;
+    static const float exp2_tab[2] = {1, M_SQRT2};
+    float exp2_val = powf(2, -63);
+    float root_val = powf(2, -32);
     for (i = -63; i < 64; i++) {
-        pow2tab[63 + i] = pow(2, i);
-        rootpow2tab[63 + i] = sqrt(pow(2, i));
+        if (!(i & 1))
+            root_val *= 2;
+        pow2tab[63 + i] = exp2_val;
+        rootpow2tab[63 + i] = root_val * exp2_tab[i & 1];
+        exp2_val *= 2;
     }
 }