From e7acc6ac3d2e7b3de434fe4571e0a4a64b777837 Mon Sep 17 00:00:00 2001
From: Mans Rullgard <mans.r...@linaro.org>
Date: Wed, 16 Nov 2011 13:48:18 -0600
Subject: [PATCH] [libpng15] Added run-time detection of ARM/NEON support

---
 pngrutil.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/pngrutil.c b/pngrutil.c
index fc450ea63..8ad1a67c5 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -3668,22 +3668,64 @@ png_read_filter_row_paeth_multibyte_pixel(png_row_infop row_info, png_bytep row,
 }
 
 #ifdef PNG_ARM_NEON
+
+#ifdef __linux__
+#include <stdio.h>
+#include <elf.h>
+#include <asm/hwcap.h>
+
+static int png_have_hwcap(unsigned cap)
+{
+   FILE *f = fopen("/proc/self/auxv", "r");
+   Elf32_auxv_t aux;
+   int have_cap = 0;
+
+   if (!f)
+      return 0;
+
+   while (fread(&aux, sizeof(aux), 1, f) > 0)
+   {
+      if (aux.a_type == AT_HWCAP &&
+          aux.a_un.a_val & cap)
+      {
+         have_cap = 1;
+         break;
+      }
+   }
+
+   fclose(f);
+
+   return have_cap;
+}
+#endif /* __linux__ */
+
 static void
 png_init_filter_functions_neon(png_structp pp, unsigned int bpp)
 {
+#ifdef __linux__
+   if (!png_have_hwcap(HWCAP_NEON))
+      return;
+#endif
+
    pp->read_filter[PNG_FILTER_VALUE_UP-1] = png_read_filter_row_up_neon;
 
-   if (bpp == 3) {
+   if (bpp == 3)
+   {
       pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub3_neon;
       pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg3_neon;
-      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] = png_read_filter_row_paeth3_neon;
-   } else if (bpp == 4) {
+      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] = 
+         png_read_filter_row_paeth3_neon;
+   }
+
+   else if (bpp == 4)
+   {
       pp->read_filter[PNG_FILTER_VALUE_SUB-1] = png_read_filter_row_sub4_neon;
       pp->read_filter[PNG_FILTER_VALUE_AVG-1] = png_read_filter_row_avg4_neon;
-      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] = png_read_filter_row_paeth4_neon;
+      pp->read_filter[PNG_FILTER_VALUE_PAETH-1] =
+          png_read_filter_row_paeth4_neon;
    }
 }
-#endif
+#endif /* PNG_ARM_NEON */
 
 static void
 png_init_filter_functions(png_structp pp)