Move CLZ emulation to common code

Move the CLZ instruction emulation C code to the common directory, so it
can be reused for all CPU cores missing a CLZ instruction (e.g. CortexM0).

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=none
TEST=run EC console on STM32F072B Discovery board with Cortex-M0 core,
and pass all available unit-tests on target.

Change-Id: Ief56cac7430fcb0fbced8a8925250c89cbd0bcfc
Reviewed-on: https://chromium-review.googlesource.com/188981
Reviewed-by: Alec Berg <alecaberg@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/common/clz.c b/common/clz.c
new file mode 100644
index 0000000000..30c987e367
--- /dev/null
+++ b/common/clz.c
@@ -0,0 +1,42 @@
+/* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Software emulation for CLZ instruction
+ */
+
+/**
+ * Count leading zeros
+ *
+ * @param x non null integer.
+ * @return the number of leading 0-bits in x,
+ * starting at the most significant bit position.
+ */
+int __clzsi2(int x)
+{
+	int r = 0;
+
+	if (!x)
+		return 32;
+	if (!(x & 0xffff0000u)) {
+		x <<= 16;
+		r += 16;
+	}
+	if (!(x & 0xff000000u)) {
+		x <<= 8;
+		r += 8;
+	}
+	if (!(x & 0xf0000000u)) {
+		x <<= 4;
+		r += 4;
+	}
+	if (!(x & 0xc0000000u)) {
+		x <<= 2;
+		r += 2;
+	}
+	if (!(x & 0x80000000u)) {
+		x <<= 1;
+		r += 1;
+	}
+	return r;
+}