Add zabs, zadd, zdiv, zmod, zmodmul, zmodpow, zneg, zpow, zsub, and the newly introduced zmodsqr

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

1 files changed, 70 insertions, 0 deletions

diff --git a/src/zsub.c b/src/zsub.c
new file mode 100644
index 0000000..437e329
--- /dev/null
+++ b/src/zsub.c
@@ -0,0 +1,70 @@
+/* See LICENSE file for copyright and license details. */
+#include "internals"
+
+#include <stdlib.h>
+#include <string.h>
+
+
+void
+zsub_unsigned(z_t a, z_t b, z_t c)
+{
+	int magcmp = zcmpmag(b, c);
+	z_t s;
+	size_t i, n;
+	zahl_char_t carry[] = {0, 0};
+
+	if (magcmp <= 0) {
+		if (magcmp == 0) {
+			SET_SIGNUM(a, 0);
+			return;
+		}
+		if (a != c)
+			zset(a, c);
+		*subtrahend = *b;
+	} else {
+		if (a != b)
+			zset(a, b);
+		*subtrahend = *c;
+	}
+
+	n = a->used < s->used ? a->used : s->used;
+
+	for (i = 0; i < n; i++) {
+		carry[~i & 1] = carry[i & 1] ? (a->chars[i] <= s->chars[i]) : (a->chars[i] < s->chars[i]);
+		a->chars[i] -= s->chars[i];
+		a->chars[i] -= carry[i & 1];
+	}
+
+	if (carry[i] & 1) {
+		while (!a->chars[i])
+			a->chars[i++] = ZAHL_CHAR_MAX;
+		a->chars[i] -= 1;
+	}
+	SET_SIGNUM(a, magcmp);
+}
+
+void
+zsub(z_t a, z_t b, z_t c)
+{
+	if (b == c) {
+		SET_SIGNUM(a, 0);
+	} else if (zzero(b)) {
+		zneg(a, c);
+	} else if (zzero(c)) {
+		if (a != b)
+			zset(a, b);
+	} else if ((zsignum(b) | zsignum(c)) < 0) {
+		if (zsignum(b) < 0) {
+			if (zsignum(c) < 0) {
+				zsub_unsigned(a, c, b);
+			} else {
+				zadd_unsigned(a, b, c);
+				SET_SIGNUM(a, -zsignum(a));
+			}
+		} else {
+			zadd_unsigned(a, b, c);
+		}
+	} else {
+		zsub_unsigned(a, b, c);
+	}
+}