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.

1 files changed, 7 insertions, 3 deletions

diff --git a/crc32.c b/crc32.c
index 2d20829..7503972 100644
--- 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