ac3enc: Add x86-optimized function to speed up log2_tab().

AC3DSPContext.ac3_max_msb_abs_int16() finds the maximum MSB of the absolute
value of each element in an array of int16_t.

Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/libavcodec/ac3dsp.h b/libavcodec/ac3dsp.h
index 7f13b11f3b..a4f141f2f5 100644
--- a/libavcodec/ac3dsp.h
+++ b/libavcodec/ac3dsp.h
@@ -35,6 +35,17 @@ typedef struct AC3DSPContext {
      * @param nb_coefs  number of frequency coefficients.
      */
     void (*ac3_exponent_min)(uint8_t *exp, int num_reuse_blocks, int nb_coefs);
+
+    /**
+     * Calculate the maximum MSB of the absolute value of each element in an
+     * array of int16_t.
+     * @param src input array
+     *            constraints: align 16. values must be in range [-32767,32767]
+     * @param len number of values in the array
+     *            constraints: multiple of 16 greater than 0
+     * @return    a value with the same MSB as max(abs(src[]))
+     */
+    int (*ac3_max_msb_abs_int16)(const int16_t *src, int len);
 } AC3DSPContext;
 
 void ff_ac3dsp_init    (AC3DSPContext *c);