Use ARM crc32 instructions if the ARM architecture has them.

The ARM crc32 instructions will be used only if an architecture is
explicitly specified at compile time that has those instructions.
For example, -march=armv8.1-a or -march=armv8-a+crc, or if the
machine being compiled on has the instructions, -march=native.

diff --git a/crc32.c b/crc32.c
index 2d2082904048b1a19eaeb2bfd203245e94cfc23b..7503972b5b0c27f5a1a91d4853c376aaf5ca8a5b 100644 (file)
--- a/crc32.c
+++ b/crc32.c
@@ -618,11 +618,15 @@ const z_crc_t FAR * ZEXPORT get_crc_table()
 }
 
 /* =========================================================================
- * Use ARM machine instructions if requested. This will compute the CRC about
+ * Use ARM machine instructions if available. This will compute the CRC about
  * ten times faster than the braided calculation. This code does not check for
- * the presence of the CRC instruction. Compile with care.
+ * the presence of the CRC instruction at run time. __ARM_FEATURE_CRC32 will
+ * only be defined if the compilation specifies an ARM processor architecture
+ * that has the instructions. For example, compiling with -march=armv8.1-a or
+ * -march=armv8-a+crc, or -march=native if the compile machine has the crc32
+ * instructions.
  */
-#if defined(Z_ARM_CRC32) && defined(__aarch64__) && W == 8
+#if defined(__aarch64__) && defined(__ARM_FEATURE_CRC32) && W == 8
 
 /*
    Constants empirically determined to maximize speed. These values are from