Added "int ceil_log2(int)" function

2 files changed, 26 insertions, 0 deletions

diff --git a/kernel/yosys.cc b/kernel/yosys.cc
index 109918816..4bfbe3614 100644
--- a/kernel/yosys.cc
+++ b/kernel/yosys.cc
@@ -124,6 +124,31 @@ void yosys_banner()
 	log("\n");
 }
 
+int ceil_log2(int x)
+{
+	if (x <= 0)
+		return 0;
+
+	int y = (x & (x - 1));
+	y = (y | -y) >> 31;
+
+	x |= (x >> 1);
+	x |= (x >> 2);
+	x |= (x >> 4);
+	x |= (x >> 8);
+	x |= (x >> 16);
+
+	x >>= 1;
+	x -= ((x >> 1) & 0x55555555);
+	x = (((x >> 2) & 0x33333333) + (x & 0x33333333));
+	x = (((x >> 4) + x) & 0x0f0f0f0f);
+	x += (x >> 8);
+	x += (x >> 16);
+	x = x & 0x0000003f;
+
+	return x - y;
+}
+
 std::string stringf(const char *fmt, ...)
 {
 	std::string string;
diff --git a/kernel/yosys.h b/kernel/yosys.h
index 92fa6ac19..c8bc46b65 100644
--- a/kernel/yosys.h
+++ b/kernel/yosys.h
@@ -222,6 +222,7 @@ extern bool memhasher_active;
 inline void memhasher() { if (memhasher_active) memhasher_do(); }
 
 void yosys_banner();
+int ceil_log2(int x);
 std::string stringf(const char *fmt, ...) YS_ATTRIBUTE(format(printf, 1, 2));
 std::string vstringf(const char *fmt, va_list ap);
 int readsome(std::istream &f, char *s, int n);