From 0339fa26eb233d2a756625e507ee51dd62c0562f Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Sat, 31 Jan 2015 09:47:15 -0800
Subject: [PATCH] lossless_neon: enable subtract green for aarch64

similar to:
1ba61b0 enable NEON intrinsics in aarch64 builds

vtbl1_u8 is available everywhere but Xcode-based iOS arm64 builds, use
vtbl1q_u8 there.

performance varies based on the input, 1-3% on encode was observed

(cherry picked from commit 416e1cea9b7f7a626341005cced947add7da5c54)

Change-Id: Ifec35b37eb856acfcf69ed7f16fa078cd40b7034
---
 src/dsp/lossless_neon.c | 48 ++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/src/dsp/lossless_neon.c b/src/dsp/lossless_neon.c
index 987767b5..9f8fa9da 100644
--- a/src/dsp/lossless_neon.c
+++ b/src/dsp/lossless_neon.c
@@ -259,20 +259,44 @@ static uint32_t Predictor13(uint32_t left, const uint32_t* const top) {
 //------------------------------------------------------------------------------
 // Subtract-Green Transform
 
-// vtbl? are unavailable in iOS/arm64 builds.
-#if !defined(__aarch64__)
+// vtbl?_u8 are marked unavailable for iOS arm64, use wider versions there.
+#if defined(__APPLE__) && defined(__aarch64__) && \
+    defined(__apple_build_version__)
+#define USE_VTBLQ
+#endif
 
-// 255 = byte will be zero'd
+#ifdef USE_VTBLQ
+// 255 = byte will be zeroed
+static const uint8_t kGreenShuffle[16] = {
+  1, 255, 1, 255, 5, 255, 5, 255, 9, 255, 9, 255, 13, 255, 13, 255
+};
+
+static WEBP_INLINE uint8x16_t DoGreenShuffle(const uint8x16_t argb,
+                                             const uint8x16_t shuffle) {
+  return vcombine_u8(vtbl1q_u8(argb, vget_low_u8(shuffle)),
+                     vtbl1q_u8(argb, vget_high_u8(shuffle)));
+}
+#else  // !USE_VTBLQ
+// 255 = byte will be zeroed
 static const uint8_t kGreenShuffle[8] = { 1, 255, 1, 255, 5, 255, 5, 255  };
 
+static WEBP_INLINE uint8x16_t DoGreenShuffle(const uint8x16_t argb,
+                                             const uint8x8_t shuffle) {
+  return vcombine_u8(vtbl1_u8(vget_low_u8(argb), shuffle),
+                     vtbl1_u8(vget_high_u8(argb), shuffle));
+}
+#endif  // USE_VTBLQ
+
 static void SubtractGreenFromBlueAndRed(uint32_t* argb_data, int num_pixels) {
   const uint32_t* const end = argb_data + (num_pixels & ~3);
+#ifdef USE_VTBLQ
+  const uint8x16_t shuffle = vld1q_u8(kGreenShuffle);
+#else
   const uint8x8_t shuffle = vld1_u8(kGreenShuffle);
+#endif
   for (; argb_data < end; argb_data += 4) {
     const uint8x16_t argb = vld1q_u8((uint8_t*)argb_data);
-    const uint8x16_t greens =
-        vcombine_u8(vtbl1_u8(vget_low_u8(argb), shuffle),
-                    vtbl1_u8(vget_high_u8(argb), shuffle));
+    const uint8x16_t greens = DoGreenShuffle(argb, shuffle);
     vst1q_u8((uint8_t*)argb_data, vsubq_u8(argb, greens));
   }
   // fallthrough and finish off with plain-C
@@ -281,19 +305,21 @@ static void SubtractGreenFromBlueAndRed(uint32_t* argb_data, int num_pixels) {
 
 static void AddGreenToBlueAndRed(uint32_t* argb_data, int num_pixels) {
   const uint32_t* const end = argb_data + (num_pixels & ~3);
+#ifdef USE_VTBLQ
+  const uint8x16_t shuffle = vld1q_u8(kGreenShuffle);
+#else
   const uint8x8_t shuffle = vld1_u8(kGreenShuffle);
+#endif
   for (; argb_data < end; argb_data += 4) {
     const uint8x16_t argb = vld1q_u8((uint8_t*)argb_data);
-    const uint8x16_t greens =
-        vcombine_u8(vtbl1_u8(vget_low_u8(argb), shuffle),
-                    vtbl1_u8(vget_high_u8(argb), shuffle));
+    const uint8x16_t greens = DoGreenShuffle(argb, shuffle);
     vst1q_u8((uint8_t*)argb_data, vaddq_u8(argb, greens));
   }
   // fallthrough and finish off with plain-C
   VP8LAddGreenToBlueAndRed_C(argb_data, num_pixels & 3);
 }
 
-#endif   // !__aarch64__
+#undef USE_VTBLQ
 
 #endif   // USE_INTRINSICS
 
@@ -320,11 +346,9 @@ void VP8LDspInitNEON(void) {
   VP8LPredictors[12] = Predictor12;
   VP8LPredictors[13] = Predictor13;
 
-#if !defined(__aarch64__)
   VP8LSubtractGreenFromBlueAndRed = SubtractGreenFromBlueAndRed;
   VP8LAddGreenToBlueAndRed = AddGreenToBlueAndRed;
 #endif
-#endif
 
 #endif   // WEBP_USE_NEON
 }