From 79697c75eeba01f5068412e03bc5484152f98341 Mon Sep 17 00:00:00 2001
From: Michael Brown
Date: Sun, 15 Mar 2015 19:28:05 +0000
Subject: [libc] Add ffs(), ffsl(), and ffsll()

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/include/strings.h | 81 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 77 insertions(+), 4 deletions(-)

(limited to 'src/include')

diff --git a/src/include/strings.h b/src/include/strings.h
index dec756fe3..fab26dc28 100644
--- a/src/include/strings.h
+++ b/src/include/strings.h
@@ -12,6 +12,54 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <string.h>
 #include <bits/strings.h>
 
+/**
+ * Find first (i.e. least significant) set bit
+ *
+ * @v x			Value
+ * @ret lsb		Least significant bit set in value (LSB=1), or zero
+ */
+static inline __attribute__ (( always_inline )) int
+__constant_ffsll ( unsigned long long x ) {
+	int r = 0;
+
+	if ( ! ( x & 0x00000000ffffffffULL ) ) {
+		x >>= 32;
+		r += 32;
+	}
+	if ( ! ( x & 0x0000ffffUL ) ) {
+		x >>= 16;
+		r += 16;
+	}
+	if ( ! ( x & 0x00ff ) ) {
+		x >>= 8;
+		r += 8;
+	}
+	if ( ! ( x & 0x0f ) ) {
+		x >>= 4;
+		r += 4;
+	}
+	if ( ! ( x & 0x3 ) ) {
+		x >>= 2;
+		r += 2;
+	}
+	if ( ! ( x & 0x1 ) ) {
+		x >>= 1;
+		r += 1;
+	}
+	return ( x ? ( r + 1 ) : 0 );
+}
+
+/**
+ * Find first (i.e. least significant) set bit
+ *
+ * @v x			Value
+ * @ret lsb		Least significant bit set in value (LSB=1), or zero
+ */
+static inline __attribute__ (( always_inline )) int
+__constant_ffsl ( unsigned long x ) {
+	return __constant_ffsll ( x );
+}
+
 /**
  * Find last (i.e. most significant) set bit
  *
@@ -46,10 +94,7 @@ __constant_flsll ( unsigned long long x ) {
 		x >>= 1;
 		r += 1;
 	}
-	if ( x & 0x1 ) {
-		r += 1;
-	}
-	return r;
+	return ( x ? ( r + 1 ) : 0 );
 }
 
 /**
@@ -63,9 +108,37 @@ __constant_flsl ( unsigned long x ) {
 	return __constant_flsll ( x );
 }
 
+int __ffsll ( long long x );
+int __ffsl ( long x );
 int __flsll ( long long x );
 int __flsl ( long x );
 
+/**
+ * Find first (i.e. least significant) set bit
+ *
+ * @v x			Value
+ * @ret lsb		Least significant bit set in value (LSB=1), or zero
+ */
+#define ffsll( x ) \
+	( __builtin_constant_p ( x ) ? __constant_ffsll ( x ) : __ffsll ( x ) )
+
+/**
+ * Find first (i.e. least significant) set bit
+ *
+ * @v x			Value
+ * @ret lsb		Least significant bit set in value (LSB=1), or zero
+ */
+#define ffsl( x ) \
+	( __builtin_constant_p ( x ) ? __constant_ffsl ( x ) : __ffsl ( x ) )
+
+/**
+ * Find first (i.e. least significant) set bit
+ *
+ * @v x			Value
+ * @ret lsb		Least significant bit set in value (LSB=1), or zero
+ */
+#define ffs( x ) ffsl ( x )
+
 /**
  * Find last (i.e. most significant) set bit
  *
-- 
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