fls_ffs.h

#ifndef _ASM_GENERIC_BITOPS_FLS_FFS_H_
#define _ASM_GENERIC_BITOPS_FLS_FFS_H_

#include <stdint.h>

#define BITS_PER_LONG 64

/**
 * fls - find last (most-significant) bit set
 * @x: the word to search
 *
 * This is defined the same way as ffs.
 * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
 */
static inline int fls(uint32_t x)
{
    int r = 32;

    if (!x) return 0;
    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;
}

static inline uint64_t __fls(uint64_t word)
{
    int num = BITS_PER_LONG - 1;

#if BITS_PER_LONG == 64
    if (!(word & (~0ull << 32))) {
        num -= 32;
        word <<= 32;
    }
#endif
    if (!(word & (~0ull << (BITS_PER_LONG - 16)))) {
        num -= 16;
        word <<= 16;
    }
    if (!(word & (~0ull << (BITS_PER_LONG - 8)))) {
        num -= 8;
        word <<= 8;
    }
    if (!(word & (~0ull << (BITS_PER_LONG - 4)))) {
        num -= 4;
        word <<= 4;
    }
    if (!(word & (~0ull << (BITS_PER_LONG - 2)))) {
        num -= 2;
        word <<= 2;
    }
    if (!(word & (~0ull << (BITS_PER_LONG - 1)))) num -= 1;
    return num;
}

static inline int fls64(u64 x)
{
    if (x == 0) return 0;
    return __fls(x) + 1;
}

/**
 * __ffs - find first bit in word.
 * @word: The word to search
 *
 * Undefined if no bit exists, so code should check against 0 first.
 */
static inline uint64_t __ffs(uint64_t word)
{
    int num = 0;

#if BITS_PER_LONG == 64
    if ((word & 0xffffffff) == 0) {
        num += 32;
        word >>= 32;
    }
#endif
    if ((word & 0xffff) == 0) {
        num += 16;
        word >>= 16;
    }
    if ((word & 0xff) == 0) {
        num += 8;
        word >>= 8;
    }
    if ((word & 0xf) == 0) {
        num += 4;
        word >>= 4;
    }
    if ((word & 0x3) == 0) {
        num += 2;
        word >>= 2;
    }
    if ((word & 0x1) == 0) num += 1;
    return num;
}

/**
 * ffs - find first bit set
 * @x: the word to search
 *
 * This is defined the same way as
 * the libc and compiler builtin ffs routines, therefore
 * differs in spirit from the above ffz (man ffs).
 */
static inline int ffs(int x)
{
    int r = 1;

    if (!x) return 0;
    if (!(x & 0xffff)) {
        x >>= 16;
        r += 16;
    }
    if (!(x & 0xff)) {
        x >>= 8;
        r += 8;
    }
    if (!(x & 0xf)) {
        x >>= 4;
        r += 4;
    }
    if (!(x & 3)) {
        x >>= 2;
        r += 2;
    }
    if (!(x & 1)) {
        x >>= 1;
        r += 1;
    }
    return r;
}

#endif