from_planar: make it more pretty

porting improvements from to_planar

Author: MartinPulec

src/from_planar.c

@@ -267,8 +267,9 @@ void
 decode_planar_parallel(decode_planar_func_t         *dec,
                        const struct from_planar_data d, int num_threads)
 {
-        const unsigned cpu_count =
-            num_threads == 0 ? get_cpu_core_count() : num_threads;
+        const unsigned cpu_count = num_threads == FROM_PLANAR_THREADS_AUTO
+                                       ? get_cpu_core_count()
+                                       : num_threads;
 
         struct convert_task_data data[cpu_count];
         for (size_t i = 0; i < cpu_count; ++i) {

src/from_planar.h

@@ -45,7 +45,10 @@
 extern "C" {
 #endif // __cplusplus
 
-#define FROM_PLANAR_MAX_COMP 4
+enum {
+        FROM_PLANAR_THREADS_AUTO = 0,
+        FROM_PLANAR_MAX_COMP = 4,
+};
 
 // defined also in pixfmt_conv.h
 #define DEFAULT_R_SHIFT  0
@@ -72,8 +75,8 @@ typedef void         decode_planar_func_t(struct from_planar_data d);
  * run the @ref decode_planar_func_t in parallel
  * @param dec         fn to run, must be to packed format (or set num_threads=1
  *                    if the conversion is to a planar format)
- * @param num_threads number of threads (0 = auto - use the number of logical
- *                    cores)
+ * @param num_threads number of threads or FROM_PLANAR_THREADS_AUTO to use the
+ *                    number of logical cores)
  */
 void decode_planar_parallel(decode_planar_func_t   *dec,
                             struct from_planar_data d, int num_threads);

src/video_decompress/jpegxs.cpp

@@ -141,7 +141,7 @@ jpegxs_to_uv_convert(struct state_decompress_jpegxs *s,
         d.rgb_shift[0] = s->rshift;
         d.rgb_shift[1] = s->gshift;
         d.rgb_shift[2] = s->bshift;
-        int num_threads = 0;
+        int num_threads = FROM_PLANAR_THREADS_AUTO;
         if (conv->convert == yuv420_to_i420) {
                 num_threads = 1; // no proper support for parallel decode
         }