[hackers] [libzahl] zgcd: optimisation of the first loop || Mattias Andrée

[git]

commit 2ce357e830db90b9a431362c66bdcf00e05e651e
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Wed Mar 2 21:21:11 2016 +0100
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Wed Mar 2 21:21:11 2016 +0100

    zgcd: optimisation of the first loop
    
    Signed-off-by: Mattias Andrée <maand...@kth.se>

diff --git a/src/zgcd.c b/src/zgcd.c
index 91216ac..7e65ebf 100644
--- a/src/zgcd.c
+++ b/src/zgcd.c
@@ -12,7 +12,7 @@ zgcd(z_t a, z_t b, z_t c)
         * Binary GCD algorithm.
         */
 
-       size_t shifts = 0, i = 0;
+       size_t shifts = 0, i = 0, min;
        zahl_char_t uv, bit;
        int neg;
 
@@ -36,13 +36,21 @@ zgcd(z_t a, z_t b, z_t c)
        zabs(v, c);
        neg = zsignum(b) < 0 && zsignum(c) < 0;
 
-       for (;; i++) {
-               uv = (i < u->used ? u->chars[i] : 0)
-                  | (i < v->used ? v->chars[i] : 0);
+       min = u->used < v->used ? u->used : v->used;
+       for (; i < min; i++) {
+               uv = u->chars[i] | v->used[i];
                for (bit = 1; bit; bit <<= 1, shifts++)
                        if (uv & bit)
                                goto loop_done;
        }
+       for (; i < u->used; i++)
+               for (bit = 1; bit; bit <<= 1, shifts++)
+                       if (u->chars[i] & bit)
+                               goto loop_done;
+       for (; i < v->used; i++)
+               for (bit = 1; bit; bit <<= 1, shifts++)
+                       if (v->chars[i] & bit)
+                               goto loop_done;
 loop_done:
        zrsh(u, u, shifts);
        zrsh(v, v, shifts);