ape: Unbreak adaptcoeffs computation

And simplify and explain the expression.

Fault introduced in f3fdef108eb06b1e71b29152bf6822519e787efe

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
index b028e94ad27b48601538d863745952aa2336c431..1e89a7bdb1906ccc086dd7b513b3c6f0ee52c4f8 100644 (file)
--- a/libavcodec/apedec.c
+++ b/libavcodec/apedec.c
@@ -1284,8 +1284,16 @@ static void do_apply_filter(APEContext *ctx, int version, APEFilter *f,
             /* Update the adaption coefficients */
             absres = FFABS(res);
             if (absres)
-                *f->adaptcoeffs = ((res & INT32_MIN) ^ ((~0UL) << 30)) >>
-                                  (25 + (absres <= f->avg*3) + (absres <= f->avg*4/3));
+                *f->adaptcoeffs = APESIGN(res) *
+                                  (8 << ((absres > f->avg * 3) + (absres > f->avg * 4 / 3)));
+                /* equivalent to the following code
+                    if (absres <= f->avg * 4 / 3)
+                        *f->adaptcoeffs = APESIGN(res) * 8;
+                    else if (absres <= f->avg * 3)
+                        *f->adaptcoeffs = APESIGN(res) * 16;
+                    else
+                        *f->adaptcoeffs = APESIGN(res) * 32;
+                */
             else
                 *f->adaptcoeffs = 0;