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arm: add /proc/cpuinfo based NEON detection for Android J-B

--- a/src/arm/cpu.c

+++ b/src/arm/cpu.c

@@ -37,6 +37,36 @@

 #elif ARCH_ARM

 #define NEON_HWCAP HWCAP_ARM_NEON

 #endif

+

+#elif defined(__ANDROID__)

+#include <stdio.h>

+#include <string.h>

+

+static unsigned parse_proc_cpuinfo(const char *flag) {

+    FILE *file = fopen("/proc/cpuinfo", "r");

+    if (!file)

+        return 0;

+

+    char line_buffer[120];

+    const char *line;

+

+    while ((line = fgets(line_buffer, sizeof(line_buffer), file))) {

+        if (strstr(line, flag)) {

+            fclose(file);

+            return 1;

+        }

+        // if line is incomplete seek back to avoid splitting the search

+        // string into two buffers

+        if (!strchr(line, '\n') && strlen(line) > strlen(flag)) {

+            if (fseek(file, -strlen(flag), SEEK_CUR))

+                break;

+        }

+    }

+

+    fclose(file);

+

+    return 0;

+}

 #endif

 unsigned dav1d_get_cpu_flags_arm(void) {

@@ -44,6 +74,8 @@

 #if HAVE_GETAUXVAL

     unsigned long hw_cap = getauxval(AT_HWCAP);

     flags |= (hw_cap & NEON_HWCAP) ? DAV1D_ARM_CPU_FLAG_NEON : 0;

+#elif defined(__ANDROID__)

+    flags |= parse_proc_cpuinfo("neon") ? DAV1D_ARM_CPU_FLAG_NEON : 0;

 #elif __APPLE__

     flags |= DAV1D_ARM_CPU_FLAG_NEON;

 #elif defined(_WIN32)