Avoid use of divides in print_size

Modification of print_size to avoid use of divides and especially
long long divides. Keep the binary scale factor in terms of bit
shifts instead. This should be faster, since the previous code
gave the compiler no clues that the divides where always powers
of two, preventing optimisation.

Signed-off-by: Nick Thompson <nick.thompson@ge.com>
Acked-by: Timur Tabi <timur@freescale.com>

diff --git a/lib/display_options.c b/lib/display_options.c
index 86df05d..a711425 100644 (file)
--- a/lib/display_options.c
+++ b/lib/display_options.c
@@ -46,13 +46,14 @@ int display_options (void)
 void print_size(unsigned long long size, const char *s)
 {
        unsigned long m = 0, n;
+       unsigned long long f;
        static const char names[] = {'E', 'P', 'T', 'G', 'M', 'K'};
-       unsigned long long d = 1ULL << (10 * ARRAY_SIZE(names));
+       unsigned long d = 10 * ARRAY_SIZE(names);
        char c = 0;
        unsigned int i;
 
-       for (i = 0; i < ARRAY_SIZE(names); i++, d >>= 10) {
-               if (size >= d) {
+       for (i = 0; i < ARRAY_SIZE(names); i++, d -= 10) {
+               if (size >> d) {
                        c = names[i];
                        break;
                }
@@ -63,11 +64,12 @@ void print_size(unsigned long long size, const char *s)
                return;
        }
 
-       n = size / d;
+       n = size >> d;
+       f = size & ((1ULL << d) - 1);
 
        /* If there's a remainder, deal with it */
-       if(size % d) {
-               m = (10 * (size - (n * d)) + (d / 2) ) / d;
+       if (f) {
+               m = (10ULL * f + (1ULL << (d - 1))) >> d;
 
                if (m >= 10) {
                        m -= 10;