AAC encoder: various fixes in M/S coding

[ffmpeg] / libavutil / internal.h

diff --git a/libavutil/internal.h b/libavutil/internal.h
index f86b7fb7413a65bf0ccb95b5ceb520279e9d5589..c4bcf37ab8ac67f1aded554c0ccbf0c6b366f3d9 100644 (file)
--- a/libavutil/internal.h
+++ b/libavutil/internal.h
@@ -39,6 +39,7 @@
 #include "timer.h"
 #include "cpu.h"
 #include "dict.h"
+#include "macros.h"
 #include "pixfmt.h"
 #include "version.h"
 
@@ -292,6 +293,25 @@ static av_always_inline av_const int64_t ff_rint64_clip(double a, int64_t amin,
     return res;
 }
 
+/**
+ * Compute 10^x for floating point values. Note: this function is by no means
+ * "correctly rounded", and is meant as a fast, reasonably accurate approximation.
+ * For instance, maximum relative error for the double precision variant is
+ * ~ 1e-13 for very small and very large values.
+ * This is ~2x faster than GNU libm's approach, which is still off by 2ulp on
+ * some inputs.
+ * @param x exponent
+ * @return 10^x
+ */
+static av_always_inline double ff_exp10(double x)
+{
+    return exp2(M_LOG2_10 * x);
+}
+
+static av_always_inline float ff_exp10f(float x)
+{
+    return exp2f(M_LOG2_10 * x);
+}
 
 /**
  * A wrapper for open() setting O_CLOEXEC.