[libc] Add flsll()

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

2 files changed, 64 insertions, 3 deletions

diff --git a/src/arch/i386/include/bits/strings.h b/src/arch/i386/include/bits/strings.h
new file mode 100644
index 000000000..092bcb593
--- /dev/null
+++ b/src/arch/i386/include/bits/strings.h
@@ -0,0 +1,50 @@
+#ifndef _BITS_STRINGS_H
+#define _BITS_STRINGS_H
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/**
+ * Find last (i.e. most significant) set bit
+ *
+ * @v value		Value
+ * @ret msb		Most significant bit set in value (LSB=1), or zero
+ */
+static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
+	long msb_minus_one;
+
+	/* If the input value is zero, the BSR instruction returns
+	 * ZF=1 and leaves an undefined value in the output register.
+	 * Perform this check in C rather than asm so that it can be
+	 * omitted in cases where the compiler is able to prove that
+	 * the input is non-zero.
+	 */
+	if ( value ) {
+		__asm__ ( "bsrl %1, %0"
+			  : "=r" ( msb_minus_one )
+			  : "rm" ( value ) );
+		return ( msb_minus_one + 1 );
+	} else {
+		return 0;
+	}
+}
+
+/**
+ * Find last (i.e. most significant) set bit
+ *
+ * @v value		Value
+ * @ret msb		Most significant bit set in value (LSB=1), or zero
+ */
+static inline __attribute__ (( always_inline )) int __flsll ( long long value ){
+	unsigned long high = ( value >> 32 );
+	unsigned long low = ( value >> 0 );
+
+	if ( high ) {
+		return ( 32 + __flsl ( high ) );
+	} else if ( low ) {
+		return ( __flsl ( low ) );
+	} else {
+		return 0;
+	}
+}
+
+#endif /* _BITS_STRINGS_H */
diff --git a/src/arch/x86/include/bits/strings.h b/src/arch/x86_64/include/bits/strings.h
index 62e0fbfba..6ee99a500 100644
--- a/src/arch/x86/include/bits/strings.h
+++ b/src/arch/x86_64/include/bits/strings.h
@@ -9,8 +9,8 @@ FILE_LICENCE ( GPL2_OR_LATER );
  * @v value		Value
  * @ret msb		Most significant bit set in value (LSB=1), or zero
  */
-static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
-	long msb_minus_one;
+static inline __attribute__ (( always_inline )) int __flsll ( long long value ){
+	long long msb_minus_one;
 
 	/* If the input value is zero, the BSR instruction returns
 	 * ZF=1 and leaves an undefined value in the output register.
@@ -19,7 +19,7 @@ static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
 	 * the input is non-zero.
 	 */
 	if ( value ) {
-		__asm__ ( "bsr %1, %0"
+		__asm__ ( "bsrq %1, %0"
 			  : "=r" ( msb_minus_one )
 			  : "rm" ( value ) );
 		return ( msb_minus_one + 1 );
@@ -28,4 +28,15 @@ static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
 	}
 }
 
+/**
+ * Find last (i.e. most significant) set bit
+ *
+ * @v value		Value
+ * @ret msb		Most significant bit set in value (LSB=1), or zero
+ */
+static inline __attribute__ (( always_inline )) int __flsl ( long value ) {
+
+	return __flsll ( value );
+}
+
 #endif /* _BITS_STRINGS_H */