Any comments on this? It has a fixed number of iterations (shift/compare/add) per log calculation.
>From dcc344aca503ba329ca98d1141d3724fa653cbe2 Mon Sep 17 00:00:00 2001 From: Frodo Baggins <[EMAIL PROTECTED](none)> Date: Mon, 12 Nov 2007 00:58:15 +0530 Subject: [PATCH] Modified log to base2 calculation Algorithm taken from wikipedia (http://en.wikipedia.org/wiki/Binary_logarithm). --- libparted/exception.c | 19 ++++++++++++------- 1 files changed, 12 insertions(+), 7 deletions(-) diff --git a/libparted/exception.c b/libparted/exception.c index d9425a3..5210fed 100644 --- a/libparted/exception.c +++ b/libparted/exception.c @@ -103,16 +103,21 @@ ped_exception_get_type_string (PedExceptionType ex_type) /* FIXME: move this out to the prospective math.c */ /* FIXME: this can probably be done more efficiently */ +/* + * Returns the floor form of binary logarithm for a 32 bit integer. + * -1 is returned if n is 0. + */ static int ped_log2 (int n) { - int x; - - PED_ASSERT (n > 0, return -1); - - for (x=0; 1 << x <= n; x++); - - return x - 1; + int pos = 0; + if (n >= 1<<16) { n >>= 16; pos += 16; } + if (n >= 1<< 8) { n >>= 8; pos += 8; } + if (n >= 1<< 4) { n >>= 4; pos += 4; } + if (n >= 1<< 2) { n >>= 2; pos += 2; } + if (n >= 1<< 1) { pos += 1; } + + return ((n == 0) ? (-1) : pos); } /** -- 1.4.4.4 _______________________________________________ parted-devel mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/parted-devel
