[FFmpeg-cvslog] avcodec/sanm: fix codec33/34 tile generator

[Manuel Lauss]

ffmpeg | branch: master | Manuel Lauss <manuel.lauss at gmail.com> | Fri May 30 12:34:23 2025 +0200| [b7662ddd15dc8f6db38065465a7a1087e0cae0ff] | committer: Manuel Lauss

avcodec/sanm: fix codec33/34 tile generator

Some of the calculated values were wrong and/or assigned
to the wrong pixel of the 4x4 block.
Found during testing with Rebel Assault Sega-CD release.

Signed-off-by: Manuel Lauss <manuel.lauss at gmail.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=b7662ddd15dc8f6db38065465a7a1087e0cae0ff
---

 libavcodec/sanm.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/libavcodec/sanm.c b/libavcodec/sanm.c
index 5912a8c14b..417199095d 100644
--- a/libavcodec/sanm.c
+++ b/libavcodec/sanm.c
@@ -493,14 +493,12 @@ static void codec33_gen_tiles(SANMVideoContext *ctx, int8_t param1)
         for (k = 0; k < 8; k++) {
             j = i + param1;
             l = k + param1;
-            p = (j + k) / 2;
-            j = (j + p) / 2;
-            m = l / 2;
-            n = (i + param1);
-            o = (k + param1);
-
-            *dst++ = p; *dst++ = p; *dst++ = j; *dst++ = n;
-            *dst++ = p; *dst++ = p; *dst++ = j; *dst++ = i;
+            p = (j + l) >> 1;
+            n = (j + p) >> 1;
+            m = (p + l) >> 1;
+
+            *dst++ = p; *dst++ = p; *dst++ = n; *dst++ = j;
+            *dst++ = p; *dst++ = p; *dst++ = n; *dst++ = j;
             *dst++ = m; *dst++ = m; *dst++ = p; *dst++ = j;
             *dst++ = l; *dst++ = l; *dst++ = m; *dst++ = p;
         }
@@ -510,8 +508,8 @@ static void codec33_gen_tiles(SANMVideoContext *ctx, int8_t param1)
         for (k = 0; k < 8; k++) {
             j = i + param1;
             l = k + param1;
-            n = ((j + l) / 2);
-            m = ((l + n) / 2);
+            n = (j + l) >> 1;
+            m = (l + n) >> 1;
 
             *dst++ = j; *dst++ = j; *dst++ = j; *dst++ = j;
             *dst++ = n; *dst++ = n; *dst++ = n; *dst++ = n;
@@ -524,13 +522,12 @@ static void codec33_gen_tiles(SANMVideoContext *ctx, int8_t param1)
         for (k = 0; k < 8; k++) {
             j = i + param1;
             l = k + param1;
-            m = (j + l) / 2;
-            n = (j + m) / 2;
-            o = m / 2;
-            p = j & 0xff;
+            m = (j + l) >> 1;
+            n = (j + m) >> 1;
+            o = (l + m) >> 1;
 
-            *dst++ = p; *dst++ = p; *dst++ = n; *dst++ = m;
-            *dst++ = p; *dst++ = p; *dst++ = n; *dst++ = m;
+            *dst++ = j; *dst++ = j; *dst++ = n; *dst++ = m;
+            *dst++ = j; *dst++ = j; *dst++ = n; *dst++ = m;
             *dst++ = n; *dst++ = n; *dst++ = m; *dst++ = o;
             *dst++ = m; *dst++ = m; *dst++ = o; *dst++ = l;
         }
@@ -540,8 +537,8 @@ static void codec33_gen_tiles(SANMVideoContext *ctx, int8_t param1)
         for (k = 0; k < 8; k++) {
             j = i + param1;
             l = k + param1;
-            m = (j + l) / 2;
-            n = m / 2;
+            m = (j + l) >> 1;
+            n = (l + m) >> 1;
 
             *dst++ = j; *dst++ = m; *dst++ = n; *dst++ = l;
             *dst++ = j; *dst++ = m; *dst++ = n; *dst++ = l;