int_sqrt() currently takes approximately constant time regardless of the value of the argument. By using the magnitude of the operand to set the initial conditions for the calculation the cost becomes proportional to log2 of the argument with the worst case behavior not being measurably slower than it currently is.
Signed-off-by: Michael Davidson <[email protected]> --- lib/int_sqrt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c index 1ef4cc344977..8394b0dcecd4 100644 --- a/lib/int_sqrt.c +++ b/lib/int_sqrt.c @@ -21,7 +21,7 @@ unsigned long int_sqrt(unsigned long x) if (x <= 1) return x; - m = 1UL << (BITS_PER_LONG - 2); + m = 1UL << (__fls(x) & ~1UL); while (m != 0) { b = y + m; y >>= 1; -- 2.15.0.rc1.287.g2b38de12cc-goog
