added memcmp function to make rockbox compilable with latest gcc versions without using libc

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@2304 a1c6a512-1295-4272-9138-f99709370657

firmware/common/memcmp.c

@@ -0,0 +1,113 @@
+/*
+FUNCTION
+	<<memcmp>>---compare two memory areas
+
+INDEX
+	memcmp
+
+ANSI_SYNOPSIS
+	#include <string.h>
+	int memcmp(const void *<[s1]>, const void *<[s2]>, size_t <[n]>);
+
+TRAD_SYNOPSIS
+	#include <string.h>
+	int memcmp(<[s1]>, <[s2]>, <[n]>)
+	void *<[s1]>;
+	void *<[s2]>;
+	size_t <[n]>;
+
+DESCRIPTION
+	This function compares not more than <[n]> characters of the
+	object pointed to by <[s1]> with the object pointed to by <[s2]>.
+
+
+RETURNS
+	The function returns an integer greater than, equal to or
+	less than zero 	according to whether the object pointed to by
+	<[s1]> is greater than, equal to or less than the object
+	pointed to by <[s2]>.
+
+PORTABILITY
+<<memcmp>> is ANSI C.
+
+<<memcmp>> requires no supporting OS subroutines.
+
+QUICKREF
+	memcmp ansi pure
+*/
+
+#include <string.h>
+
+
+/* Nonzero if either X or Y is not aligned on a "long" boundary.  */
+#define UNALIGNED(X, Y) \
+  (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
+
+/* How many bytes are copied each iteration of the word copy loop.  */
+#define LBLOCKSIZE (sizeof (long))
+
+/* Threshhold for punting to the byte copier.  */
+#define TOO_SMALL(LEN)  ((LEN) < LBLOCKSIZE)
+
+int
+_DEFUN (memcmp, (m1, m2, n),
+	_CONST _PTR m1 _AND
+	_CONST _PTR m2 _AND
+	size_t n)
+{
+#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
+  unsigned char *s1 = (unsigned char *) m1;
+  unsigned char *s2 = (unsigned char *) m2;
+
+  while (n--)
+    {
+      if (*s1 != *s2)
+	{
+	  return *s1 - *s2;
+	}
+      s1++;
+      s2++;
+    }
+  return 0;
+#else  
+  unsigned char *s1 = (unsigned char *) m1;
+  unsigned char *s2 = (unsigned char *) m2;
+  unsigned long *a1;
+  unsigned long *a2;
+
+  /* If the size is too small, or either pointer is unaligned,
+     then we punt to the byte compare loop.  Hopefully this will
+     not turn up in inner loops.  */
+  if (!TOO_SMALL(n) && !UNALIGNED(s1,s2))
+    {
+      /* Otherwise, load and compare the blocks of memory one 
+         word at a time.  */
+      a1 = (unsigned long*) s1;
+      a2 = (unsigned long*) s2;
+      while (n >= LBLOCKSIZE)
+        {
+          if (*a1 != *a2) 
+   	    break;
+          a1++;
+          a2++;
+          n -= LBLOCKSIZE;
+        }
+
+      /* check m mod LBLOCKSIZE remaining characters */
+
+      s1 = (char*)a1;
+      s2 = (char*)a2;
+    }
+
+  while (n--)
+    {
+      if (*s1 != *s2)
+	return *s1 - *s2;
+      s1++;
+      s2++;
+    }
+
+  return 0;
+#endif /* not PREFER_SIZE_OVER_SPEED */
+}
+