@@ -91,18 +91,35 @@ const AVClass *ff_urlcontext_child_class_iterate(void **iter)
return ret;
}
-const char *avio_enum_protocols(void **const opaque, const int output)
+#define AVIO_ENUM_PROTOCOLS(METHOD) \
+ typedef const URLProtocol *const *Iterator; \
+ for(Iterator p = *opaque ? (Iterator)(*opaque) + 1 : url_protocols; *p; ++p) { \
+ if ((*p)->METHOD) { \
+ *opaque = (void *)p; \
+ return (*p)->name; \
+ } \
+ } \
+ *opaque = NULL; \
+ return NULL;
+
+static inline
+const char *avio_enum_protocols_for_output(void **const opaque)
{
- typedef const URLProtocol *const *Iterator;
- for(Iterator p = *opaque ? (Iterator)(*opaque) + 1 : url_protocols; *p; ++p) {
- if ((output && (*p)->url_write) || (!output && (*p)->url_read)) {
- *opaque = (void *)p;
- return (*p)->name;
- }
- }
+ AVIO_ENUM_PROTOCOLS(url_write);
+}
- *opaque = NULL;
- return NULL;
+static inline
+const char *avio_enum_protocols_for_input(void **const opaque)
+{
+ AVIO_ENUM_PROTOCOLS(url_read);
+}
+
+const char *avio_enum_protocols(void **const opaque, const int output)
+{
+ if (output)
+ return avio_enum_protocols_for_output(opaque);
+ else
+ return avio_enum_protocols_for_input(opaque);
}
const AVClass *avio_protocol_get_class(const char *name)
The function 'avio_enum_protocols()' iterates through the list of protocols, looking for a protocol that has a certain non-zero pointer-to-function; the exact pointer-to-function to use depends on the the argument passed through the parameter 'output'. * Before this commit, the parameter 'output' was being checked on every iteration, despite the fact that its value does not change. * This commit explicitly separates out the different cases into their own loops (i.e., their own functions), so that 'output' need not be tested on each iteration. * To aid maintenance, these separate functions are the expansion of a single macro that provides a generic implementation: AVIO_ENUM_PROTOCOLS(METHOD) One of the benefits of using a macro is that it does not depend on a compiler being able to optimize the code. Before deciding to use a macro for this purpose, it was attempted to write a generic version in terms of pure C code that also would not rely on magical optimizations; this involved type conversions on pointer arithmetic around 'offsetof()', but it turns out that Standard C (not to be confused with Actual C) has no reliable way to recover the value of a pointer-to-function from an object, so that avenue was ultimately abandoned for the sake of pure pedantry. --- libavformat/protocols.c | 37 +++++++++++++++++++++++++++---------- 1 file changed, 27 insertions(+), 10 deletions(-)