The new version do few 64 bits operations. When high 32 bits of dividend becomes 0, use 32 bits division directly.
Signed-off-by: Zhaoxiu Zeng <[email protected]> --- lib/div64.c | 63 +++++++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 43 insertions(+), 20 deletions(-) diff --git a/lib/div64.c b/lib/div64.c index 4382ad7..89b9ed4 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -23,37 +23,60 @@ /* Not needed on 64bit architectures */ #if BITS_PER_LONG == 32 +typedef union { + struct { +#if defined(__LITTLE_ENDIAN) + uint32_t vl; + uint32_t vh; +#else + uint32_t vh; + uint32_t vl; +#endif + } u; + uint64_t v; +} UINT64; + uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base) { - uint64_t rem = *n; - uint64_t b = base; - uint64_t res, d = 1; - uint32_t high = rem >> 32; + UINT64 rem = { .v = *n, }; + UINT64 res, b; + int shift; + uint32_t d; /* Reduce the thing a bit first */ - res = 0; - if (high >= base) { - high /= base; - res = (uint64_t) high << 32; - rem -= (uint64_t) (high*base) << 32; + res.v = 0; + if (rem.u.vh >= base) { + res.u.vh = rem.u.vh / base; + rem.u.vh = rem.u.vh % base; + if (!rem.u.vh) + goto end; } - while ((int64_t)b > 0 && b < rem) { - b = b+b; - d = d+d; - } + /* + * Here rem.u.vh < base, so "fls(rem.u.vh) <= fls(base)". + * If "fls(rem.u.vh) == fls(base)", shift equals 31. + * else, shift equals "32 + fls(rem.u.vh) - fls(base)" + */ + shift = 32 + fls(rem.u.vh) - fls(base) - (fls(rem.u.vh) == fls(base)); + b.u.vl = base << shift; + b.u.vh = base >> (32 - shift); + d = 1UL << shift; do { - if (rem >= b) { - rem -= b; - res += d; + if (rem.v >= b.v) { + rem.v -= b.v; + res.u.vl |= d; } - b >>= 1; + b.v >>= 1; d >>= 1; - } while (d); + } while (rem.u.vh); + +end: + res.u.vl |= rem.u.vl / base; + rem.u.vl = rem.u.vl % base; - *n = res; - return rem; + *n = res.v; + return rem.u.vl; } EXPORT_SYMBOL(__div64_32); -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
