msp430_common: Add supplemental __clzhi2, __ctzhi2, for old MSPGCC

cpu/msp430_common/mspgcc-supplement.c

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2016 Eistec AB
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu
+ * @{
+ *
+ * @file
+ * @brief       MSPGCC supplemental functions
+ *
+ * @author      Joakim Nohlgård <joakim.nohlgard@eistec.se
+ *
+ * @}
+ */
+
+#ifdef __MSPGCC__
+
+/* internal GCC type for "half integer" (16 bit) */
+/* See also:
+ * http://stackoverflow.com/questions/4559025/what-does-gcc-attribute-modexx-actually-do
+ * http://www.delorie.com/gnu/docs/gcc/gccint_53.html
+ */
+typedef unsigned int UHItype __attribute__ ((mode (HI)));
+
+/**
+ * @brief Count leading zeros
+ *
+ * Naive implementation
+ */
+int __clzhi2(UHItype x)
+{
+    int i = 0;
+    for (UHItype mask = (1 << 15); mask != 0; mask >>= 1) {
+        if (x & mask) {
+            return i;
+        }
+        ++i;
+    }
+    return i; /* returns 16 if x == 0 */
+}
+
+/**
+ * @brief Count trailing zeros
+ *
+ * Naive implementation
+ */
+int __ctzhi2(UHItype x)
+{
+    int i = 0;
+    for (UHItype mask = 1; mask != 0; mask <<= 1) {
+        if (x & mask) {
+            return i;
+        }
+        ++i;
+    }
+    return i; /* returns 16 if x == 0 */
+}
+#endif /* __MSPGCC__ */