AP_HAL: added replacement for memrchr()

libraries/AP_HAL/utility/replace.cpp

@@ -0,0 +1,22 @@
+/*
+  replacement functions for systems that are missing required library functions
+ */
+
+#include "replace.h"
+
+#ifndef HAVE_MEMRCHR
+/*
+  replacement for memrchr(). Note that we make the buffer non-const to
+  avoid issues with converting const to non-const
+ */
+void *replace_memrchr(void *s, int c, size_t n)
+{
+    uint8_t *b = (uint8_t *)s;
+    for (int32_t i=n-1; i>=0; i--) {
+        if (b[i] == (uint8_t)c) {
+            return (void *)&b[i];
+        }
+    }
+    return nullptr;
+}
+#endif

libraries/AP_HAL/utility/replace.h

@@ -0,0 +1,12 @@
+/*
+  replacement functions for systems that are missing required library functions
+ */
+
+#pragma once
+
+#include <AP_HAL/AP_HAL.h>
+
+#ifndef HAVE_MEMRCHR
+void *replace_memrchr(void *s, int c, size_t n);
+#define memrchr(s,c,n) replace_memrchr(s,c,n)
+#endif