---
name: "fls64"
section: "9"
platform: "linux"
package: "linux-manual-4.9"
version: "4.9.228-1"
release: "Debian 9 (Stretch)"
platforms: ["linux"]
url: "https://new.carta.tech/fls64"
---

# fls64(9)

find last set bit in a 64-bit word

## NAME

fls64 - find last set bit in a 64-bit word

## SYNOPSIS

**int fls64(\_\_u64** *x***);**

## ARGUMENTS

*x*

the word to search

## DESCRIPTION

This is defined in a similar way as the libc and compiler builtin ffsll, but returns the position of the most significant set bit.

fls64(value) returns 0 if value is 0 or the position of the last set bit if value is nonzero. The last (most significant) bit is at position 64.

## COPYRIGHT