Capture CRC content for deferred-loading cores

== DETAILS

Fixes a bug where content CRC32 is not calculated when content loading
is done by the core instead of libretro. This impacts the ability to
do accurate content matching on netplay.

This notably affects MAME, but is by no means limited to MAME.

Change summary:
- adds a method to the crc32 implementation that calculates crc32 for
  a file (as opposed to an in-memory buffer)
- fix a minor bug that would print the "core will load its own content"
  right before attempting to load compressed content
- in the actual "core will load its own content" path, calculate the CRC32
  and log it before returning

== TESTING
Tested locally on OSX:
- loaded content
- started netplay
- confirmed CRC showing in netplay data
- verified CRC32 against external crc32 tool

libretro-common/encodings/encoding_crc32.c

@@ -23,6 +23,8 @@
 #include <stdint.h>
 #include <stddef.h>
 #include <encodings/crc32.h>
+#include <streams/file_stream.h>
+#include <stdlib.h>
 
 static const uint32_t crc32_table[256] = {
   0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
@@ -88,3 +90,18 @@ uint32_t encoding_crc32(uint32_t crc, const uint8_t *buf, size_t len)
 
    return crc ^ 0xffffffff;
 }
+
+uint32_t file_crc32(uint32_t crc, const char *path) {
+   if(path == NULL)
+     return 0;
+
+   void *file_bytes = NULL;
+   int64_t file_len = 0;
+
+   if(filestream_read_file(path, &file_bytes, &file_len)) {
+     crc = encoding_crc32(crc, (uint8_t *)file_bytes, file_len);
+     free(file_bytes);
+     return crc;
+   }
+   return 0;
+}

libretro-common/include/encodings/crc32.h

@@ -31,6 +31,7 @@
 RETRO_BEGIN_DECLS
 
 uint32_t encoding_crc32(uint32_t crc, const uint8_t *buf, size_t len);
+uint32_t file_crc32(uint32_t crc, const char *path);
 
 RETRO_END_DECLS
 

libretro-common/streams/file_stream.c

@@ -482,7 +482,8 @@ int filestream_close(RFILE *stream)
  *
  * Read the contents of a file into @buf.
  *
- * Returns: number of items read, -1 on error.
+ * Returns: 1 on success, 0 on failure
+ * In the error case, the dereferenced buf is set to NULL and the len is set to -1.
  */
 int64_t filestream_read_file(const char *path, void **buf, int64_t *len)
 {

tasks/task_content.c

@@ -603,9 +603,6 @@ static bool content_file_load(
       }
       else
       {
-         RARCH_LOG("%s\n",
-               msg_hash_to_str(
-                  MSG_CONTENT_LOADING_SKIPPED_IMPLEMENTATION_WILL_DO_IT));
 
 #ifdef HAVE_COMPRESSION
          if (     !content_ctx->block_extract
@@ -619,6 +616,9 @@ static bool content_file_load(
             goto error;
 #endif
       }
+      RARCH_LOG("%s\n", msg_hash_to_str(MSG_CONTENT_LOADING_SKIPPED_IMPLEMENTATION_WILL_DO_IT));
+      content_rom_crc = file_crc32(0, path);
+      RARCH_LOG("CRC32: 0x%x .\n", (unsigned)content_rom_crc);
    }
 
    load_info.content = content;