From c5941a2731516c365ec30db0b0723c4edbb3f9c7 Mon Sep 17 00:00:00 2001
From: rsdy <p@symmetree.dev>
Date: Fri, 8 Oct 2021 12:45:04 +0100
Subject: [PATCH] Make the C implementation default to using NEON on aarch64

---
 c/Makefile.testing |  4 ++++
 c/README.md        | 15 ++++++++++++---
 c/blake3_impl.h    |  4 ++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/c/Makefile.testing b/c/Makefile.testing
index 41e6b82..b85aedf 100644
--- a/c/Makefile.testing
+++ b/c/Makefile.testing
@@ -42,6 +42,10 @@ EXTRAFLAGS += -DBLAKE3_USE_NEON
 TARGETS += blake3_neon.o
 endif
 
+ifdef BLAKE3_NO_NEON
+EXTRAFLAGS += -DBLAKE3_NO_NEON
+endif
+
 all: blake3.c blake3_dispatch.c blake3_portable.c main.c $(TARGETS)
 	$(CC) $(CFLAGS) $(EXTRAFLAGS) $^ -o $(NAME) $(LDFLAGS)
 
diff --git a/c/README.md b/c/README.md
index 5268818..418a5ab 100644
--- a/c/README.md
+++ b/c/README.md
@@ -250,15 +250,24 @@ gcc -shared -O3 -o libblake3.so -DBLAKE3_NO_SSE2 -DBLAKE3_NO_SSE41 -DBLAKE3_NO_A
 
 ## ARM NEON
 
-The NEON implementation is not enabled by default on ARM, since not all
-ARM targets support it. To enable it, set `BLAKE3_USE_NEON=1`. Here's an
-example of building a shared library on ARM Linux with NEON support:
+The NEON implementation is enabled by default on AARCH64, but not on
+other ARM targets, since not all of them support it. To enable it, set
+`BLAKE3_USE_NEON=1`. Here's an example of building a shared library on
+ARM Linux with NEON support:
 
 ```bash
 gcc -shared -O3 -o libblake3.so -DBLAKE3_USE_NEON blake3.c blake3_dispatch.c \
     blake3_portable.c blake3_neon.c
 ```
 
+To explicitiy disable using NEON instructions on AARCH64, set
+`BLAKE3_NO_NEON=1`.
+
+```bash
+gcc -shared -O3 -o libblake3.so -DBLAKE3_NO_NEON blake3.c blake3_dispatch.c \
+    blake3_portable.c 
+```
+
 Note that on some targets (ARMv7 in particular), extra flags may be
 required to activate NEON support in the compiler. If you see an error
 like...
diff --git a/c/blake3_impl.h b/c/blake3_impl.h
index 86ab6aa..8688479 100644
--- a/c/blake3_impl.h
+++ b/c/blake3_impl.h
@@ -45,6 +45,10 @@ enum blake3_flags {
 #include <immintrin.h>
 #endif
 
+#if defined(__aarch64__) && !defined(BLAKE3_NO_NEON) && !defined(BLAKE3_USE_NEON)
+#define BLAKE3_USE_NEON
+#endif
+
 #if defined(IS_X86)
 #define MAX_SIMD_DEGREE 16
 #elif defined(BLAKE3_USE_NEON)