[hackers] [libzahl] Optimise zdivmod || Mattias Andrée

[git]

commit 6cc727a4a17c6b037f665433cc47b37aa926b92b
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Thu Mar 3 12:52:25 2016 +0100
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Thu Mar 3 12:52:25 2016 +0100

    Optimise zdivmod
    
    Signed-off-by: Mattias Andrée <maand...@kth.se>

diff --git a/src/internals.h b/src/internals.h
index db45a3b..89d98e1 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -26,8 +26,7 @@
        X(libzahl_tmp_modsqr)\
        X(libzahl_tmp_divmod_a)\
        X(libzahl_tmp_divmod_b)\
-       X(libzahl_tmp_divmod_d)\
-       X(libzahl_tmp_divmod_e)
+       X(libzahl_tmp_divmod_d)
 
 #define LIST_CONSTS\
        X(libzahl_const_1e19, zsetu, 10000000000000000000ULL) /* The largest 
power of 10 < 2⁶⁴. */\
diff --git a/src/zdivmod.c b/src/zdivmod.c
index c25ae49..052e343 100644
--- a/src/zdivmod.c
+++ b/src/zdivmod.c
@@ -4,13 +4,12 @@
 #define ta  libzahl_tmp_divmod_a
 #define tb  libzahl_tmp_divmod_b
 #define td  libzahl_tmp_divmod_d
-#define te  libzahl_tmp_divmod_e
 
 
 void
 zdivmod(z_t a, z_t b, z_t c, z_t d)
 {
-       size_t c_bits, d_bits, shift;
+       size_t c_bits, d_bits, bit;
        int sign, cmpmag;
 
        sign = zsignum(c) * zsignum(d);
@@ -47,25 +46,24 @@ zdivmod(z_t a, z_t b, z_t c, z_t d)
        c_bits = zbits(c);
        d_bits = zbits(d);
 
-       shift = c_bits - d_bits;
-       zlsh(td, d, shift);
+       bit = c_bits - d_bits;
+       zlsh(td, d, bit);
        SET_SIGNUM(td, 1);
        if (zcmpmag(td, c) > 0) {
                zrsh(td, td, 1);
-               shift -= 1;
+               bit -= 1;
        }
 
-       zsetu(te, 1);
-       zlsh(te, te, shift);
        SET_SIGNUM(ta, 0);
        zabs(tb, c);
 
-       while (!zzero(te)) {
+       for (;;) {
                if (zcmpmag(td, tb) <= 0) {
                        zsub(tb, tb, td);
-                       zor(ta, ta, te);
+                       zbset(ta, ta, bit, 1);
                }
-               zrsh(te, te, 1);
+               if (!bit--)
+                       break;
                zrsh(td, td, 1);
        }