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

[git]

commit 56680b5fa737dd7aa1cd7446cad62f5b1da2235c
Author:     Mattias Andrée <maand...@kth.se>
AuthorDate: Thu Mar 3 12:23:39 2016 +0100
Commit:     Mattias Andrée <maand...@kth.se>
CommitDate: Thu Mar 3 12:23:39 2016 +0100

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

diff --git a/src/internals.h b/src/internals.h
index 44b6214..db45a3b 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -23,7 +23,11 @@
        X(libzahl_tmp_pow_b)\
        X(libzahl_tmp_pow_c)\
        X(libzahl_tmp_pow_d)\
-       X(libzahl_tmp_modsqr)
+       X(libzahl_tmp_modsqr)\
+       X(libzahl_tmp_divmod_a)\
+       X(libzahl_tmp_divmod_b)\
+       X(libzahl_tmp_divmod_d)\
+       X(libzahl_tmp_divmod_e)
 
 #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
new file mode 100644
index 0000000..c25ae49
--- /dev/null
+++ b/src/zdivmod.c
@@ -0,0 +1,75 @@
+/* See LICENSE file for copyright and license details. */
+#include "internals"
+
+#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;
+       int sign, cmpmag;
+
+       sign = zsignum(c) * zsignum(d);
+
+       if (!sign) {
+               if (zzero(c)) {
+                       if (zzero(d)) {
+                               errno = EDOM; /* Indeterminate form: 0 divided 
by 0 */
+                               FAILURE_JUMP();
+                       } else {
+                               SET_SIGNUM(a, 0);
+                               SET_SIGNUM(b, 0);
+                       }
+               } else {
+                       errno = EDOM; /* Undefined form: Division by 0 */
+                       FAILURE_JUMP();
+               }
+               return;
+       } else if ((cmpmag = zcmpmag(c, d)) <= 0) {
+               if (cmpmag == 0) {
+                       zseti(a, sign);
+                       SET_SIGNUM(b, 0);
+                       return;
+               } else if (sign < 0) {
+                       zsub_unsigned(b, d, c);
+               } else if (b != c) {
+                       zset(b, c);
+               }
+               SET_SIGNUM(b, 1);
+               SET_SIGNUM(a, 0);
+               return;
+       }
+
+       c_bits = zbits(c);
+       d_bits = zbits(d);
+
+       shift = c_bits - d_bits;
+       zlsh(td, d, shift);
+       SET_SIGNUM(td, 1);
+       if (zcmpmag(td, c) > 0) {
+               zrsh(td, td, 1);
+               shift -= 1;
+       }
+
+       zsetu(te, 1);
+       zlsh(te, te, shift);
+       SET_SIGNUM(ta, 0);
+       zabs(tb, c);
+
+       while (!zzero(te)) {
+               if (zcmpmag(td, tb) <= 0) {
+                       zsub(tb, tb, td);
+                       zor(ta, ta, te);
+               }
+               zrsh(te, te, 1);
+               zrsh(td, td, 1);
+       }
+
+       zset(a, ta);
+       zset(b, tb);
+       SET_SIGNUM(a, sign);
+}