shorten comments for pr #390

src/random.c

@@ -160,7 +160,7 @@ uintptr_t _mi_random_next(mi_random_ctx_t* ctx) {
 /* ----------------------------------------------------------------------------
 To initialize a fresh random context we rely on the OS:
 - Windows     : BCryptGenRandom (or RtlGenRandom)
-- macOS       : CCRandomGenerateBytes
+- macOS       : CCRandomGenerateBytes, arc4random_buf
 - bsd,wasi    : arc4random_buf
 - Linux       : getrandom,/dev/urandom
 If we cannot get good randomness, we fall back to weak randomness based on a timer and ASLR.
@@ -194,34 +194,22 @@ static bool os_random_buf(void* buf, size_t buf_len) {
 
 #elif defined(__APPLE__)
 #include <AvailabilityMacros.h>
-#if defined(MAC_OS_X_VERSION_10_10) && \
-    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
+#if defined(MAC_OS_X_VERSION_10_10) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
 #include <CommonCrypto/CommonRandom.h>
 #endif
 static bool os_random_buf(void* buf, size_t buf_len) {
-  /* The implementation of arc4random_buf(3) differs from its documentation.
-   * It is documented as "always successful, and no return value is reserved
-   * to indicate an error." However, the actual implementation invokes the
-   * function "ccrng_generate" without validating the error cases. It might
-   * fail silently, which leads to unexpected source of entropy.
-   * See:
-   *   https://opensource.apple.com/source/Libc/Libc-1439.40.11/gen/FreeBSD/arc4random.c.auto.html
-   *
-   * CCRandomGenerateBytes(), on the contrary, returns cryptographically strong
-   * random bits with explicit status code.
-   */
-#if defined(MAC_OS_X_VERSION_10_15) && \
-    MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_15
-  return CCRandomGenerateBytes(buf, buf_len) == kCCSuccess;
-#else
-  /* Prior to macOS 10.15, CCRandomGenerateBytes() might take a bit longer time
-   * to complete, so failback to arc4random_buf().
-   */
-  arc4random_buf(buf, buf_len);
-  return true;
-#endif
+  #if defined(MAC_OS_X_VERSION_10_15) && MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_15
+    // We prefere CCRandomGenerateBytes as it returns an error code while arc4random_buf
+    // may fail silently on macOS. See PR #390, and <https://opensource.apple.com/source/Libc/Libc-1439.40.11/gen/FreeBSD/arc4random.c.auto.html>      
+    return (CCRandomGenerateBytes(buf, buf_len) == kCCSuccess);
+  #else
+    // fall back on older macOS
+    arc4random_buf(buf, buf_len);
+    return true;
+  #endif
 }
-#elif defined(ANDROID) || defined(__DragonFly__) || \
+
+#elif defined(__ANDROID__) || defined(__DragonFly__) || \
       defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__) || \
       defined(__sun) // todo: what to use with __wasi__?
 #include <stdlib.h>