libzahl

commit 56680b5fa737dd7aa1cd7446cad62f5b1da2235c
parent 0e905d00aceaa79849c25d359d7b7a6ee79175d7
Author: Mattias Andrée <maandree@kth.se>
Date:   Thu,  3 Mar 2016 12:23:39 +0100

Add zdivmod

Signed-off-by: Mattias Andrée <maandree@kth.se>

Diffstat:
M
src/internals.h
 | 
6
+++++-
A
src/zdivmod.c
 | 
75
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 80 insertions(+), 1 deletion(-)
diff --git 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
@@ -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);
+}