audio: simplify further

Drop mp_chmap_diff() (which is unused too now), and implement
mp_chmap_diffn() in a slightly simpler way. (Too bad there is no
standard function for counting set bits.)

(cherry picked from commit 00130651dac758f90bf98306a9d1e569ed4155ca)

2 files changed, 8 insertions, 16 deletions

diff --git a/audio/chmap.c b/audio/chmap.c
index 4f76eedd59..4fd43e3bc7 100644
--- a/audio/chmap.c
+++ b/audio/chmap.c
@@ -395,26 +395,20 @@ void mp_chmap_get_reorder(int src[MP_NUM_CHANNELS], const struct mp_chmap *from,
         assert(src[n] < 0 || (to->speaker[n] == from->speaker[src[n]]));
 }
 
-// Return channels that are only in a.
-// Performs the difference between a and b, and store it in diff. If b has
-// channels that do not appear in a, those will not appear in the difference.
-// To get to those the argument ordering in the function call has to be
-// inverted. For the same reason, the diff with a superset will return no
-// speakers.
-void mp_chmap_diff(const struct mp_chmap *a, const struct mp_chmap *b,
-                   struct mp_chmap *diff)
+static int popcount64(uint64_t bits)
 {
-    uint64_t a_mask = mp_chmap_to_lavc_unchecked(a);
-    uint64_t b_mask = mp_chmap_to_lavc_unchecked(b);
-    mp_chmap_from_lavc(diff, (a_mask ^ b_mask) & a_mask);
+    int r = 0;
+    for (int n = 0; n < 64; n++)
+        r += !!(bits & (1ULL << n));
+    return r;
 }
 
 // Return the number of channels only in a.
 int mp_chmap_diffn(const struct mp_chmap *a, const struct mp_chmap *b)
 {
-    struct mp_chmap diff;
-    mp_chmap_diff(a, b, &diff);
-    return diff.num;
+    uint64_t a_mask = mp_chmap_to_lavc_unchecked(a);
+    uint64_t b_mask = mp_chmap_to_lavc_unchecked(b);
+    return popcount64((a_mask ^ b_mask) & a_mask);
 }
 
 // Returns something like "fl-fr-fc". If there's a standard layout in lavc
diff --git a/audio/chmap.h b/audio/chmap.h
index c3826065ce..adb7481665 100644
--- a/audio/chmap.h
+++ b/audio/chmap.h
@@ -123,8 +123,6 @@ void mp_chmap_reorder_to_lavc(struct mp_chmap *map);
 void mp_chmap_get_reorder(int src[MP_NUM_CHANNELS], const struct mp_chmap *from,
                           const struct mp_chmap *to);
 
-void mp_chmap_diff(const struct mp_chmap *a, const struct mp_chmap *b,
-                   struct mp_chmap *diff);
 int mp_chmap_diffn(const struct mp_chmap *a, const struct mp_chmap *b);
 
 char *mp_chmap_to_str_buf(char *buf, size_t buf_size, const struct mp_chmap *src);