[arm] Add optimised string functions for 64-bit ARM

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/arm64/include/bits/string.h

@@ -0,0 +1,106 @@
+#ifndef BITS_STRING_H
+#define BITS_STRING_H
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * String functions
+ *
+ */
+
+extern void arm64_bzero ( void *dest, size_t len );
+extern void arm64_memset ( void *dest, size_t len, int character );
+extern void arm64_memcpy ( void *dest, const void *src, size_t len );
+extern void arm64_memmove_forwards ( void *dest, const void *src, size_t len );
+extern void arm64_memmove_backwards ( void *dest, const void *src, size_t len );
+extern void arm64_memmove ( void *dest, const void *src, size_t len );
+
+/**
+ * Fill memory region
+ *
+ * @v dest		Destination region
+ * @v character		Fill character
+ * @v len		Length
+ * @ret dest		Destination region
+ */
+static inline __attribute__ (( always_inline )) void *
+memset ( void *dest, int character, size_t len ) {
+
+	/* Allow gcc to generate inline "stX xzr" instructions for
+	 * small, constant lengths.
+	 */
+	if ( __builtin_constant_p ( character ) && ( character == 0 ) &&
+	     __builtin_constant_p ( len ) && ( len <= 64 ) ) {
+		__builtin_memset ( dest, 0, len );
+		return dest;
+	}
+
+	/* For zeroing larger or non-constant lengths, use the
+	 * optimised variable-length zeroing code.
+	 */
+	if ( __builtin_constant_p ( character ) && ( character == 0 ) ) {
+		arm64_bzero ( dest, len );
+		return dest;
+	}
+
+	/* Not necessarily zeroing: use basic variable-length code */
+	arm64_memset ( dest, len, character );
+	return dest;
+}
+
+/**
+ * Copy memory region
+ *
+ * @v dest		Destination region
+ * @v src		Source region
+ * @v len		Length
+ * @ret dest		Destination region
+ */
+static inline __attribute__ (( always_inline )) void *
+memcpy ( void *dest, const void *src, size_t len ) {
+
+	/* Allow gcc to generate inline "ldX"/"stX" instructions for
+	 * small, constant lengths.
+	 */
+	if ( __builtin_constant_p ( len ) && ( len <= 64 ) ) {
+		__builtin_memcpy ( dest, src, len );
+		return dest;
+	}
+
+	/* Otherwise, use variable-length code */
+	arm64_memcpy ( dest, src, len );
+	return dest;
+}
+
+/**
+ * Copy (possibly overlapping) memory region
+ *
+ * @v dest		Destination region
+ * @v src		Source region
+ * @v len		Length
+ * @ret dest		Destination region
+ */
+static inline __attribute__ (( always_inline )) void *
+memmove ( void *dest, const void *src, size_t len ) {
+	ssize_t offset = ( dest - src );
+
+	/* If required direction of copy is known at build time, then
+	 * use the appropriate forwards/backwards copy directly.
+	 */
+	if ( __builtin_constant_p ( offset ) ) {
+		if ( offset <= 0 ) {
+			arm64_memmove_forwards ( dest, src, len );
+			return dest;
+		} else {
+			arm64_memmove_backwards ( dest, src, len );
+			return dest;
+		}
+	}
+
+	/* Otherwise, use ambidirectional copy */
+	arm64_memmove ( dest, src, len );
+	return dest;
+}
+
+#endif /* BITS_STRING_H */