1 files changed, 94 insertions, 0 deletions
diff --git a/src/zadd.c b/src/zadd.c
new file mode 100644
index 0000000..dd3a8c6
--- /dev/null
+++ b/src/zadd.c
@@ -0,0 +1,94 @@
+/* See LICENSE file for copyright and license details. */
+#include "internals"
+
+#include <stdlib.h>
+#include <string.h>
+
+
+void
+zadd_unsigned(z_t a, z_t b, z_t c)
+{
+	size_t i, size, n;
+	uint32_t carry[] = {0, 0};
+	zahl_char_t *addend;
+
+	if (a == c) {
+		zadd_unsigned(a, c, b);
+		return;
+	}
+
+	size = b->used > c->used ? b->used : c->used;
+	if (a->alloced < size + 1) {
+		a->alloced = size + 1;
+		a->chars = realloc(a->chars, a->alloced * sizeof(*(a->chars)));
+	}
+	a->chars[size] = 0;
+
+	n = b->used + c->used - size;
+	if (a == b) {
+		if (a->used < c->used) {
+			n = c->used;
+			memset(a->chars + a->used, 0, (n - a->used) * sizeof(*(a->chars)));
+		}
+		addend = c->chars;
+	} else if (a == c) {
+		if (a->used < b->used) {
+			n = b->used;
+			memset(a->chars + a->used, 0, (n - a->used) * sizeof(*(a->chars)));
+		}
+		addend = b->chars;
+	} else if (b->used > c->used) {
+		memcpy(a->chars, b->chars, b->used * sizeof(*(a->chars)));
+		a->used = b->used;
+		addend = c->chars;
+	} else {
+		memcpy(a->chars, c->chars, c->used * sizeof(*(a->chars)));
+		a->used = c->used;
+		addend = b->chars;
+	}
+
+	for (i = 0; i < n; i++) {
+		if (carry[i & 1])
+			carry[~i & 1] = (ZAHL_CHAR_MAX - a->chars[i] <= addend[i]);
+		else
+			carry[~i & 1] = (ZAHL_CHAR_MAX - a->chars[i] < addend[i]);
+		a->chars[i] += addend[i] + carry[i & 1];
+	}
+
+	while (carry[~i & 1]) {
+		carry[i & 1] = a->chars[i] == ZAHL_CHAR_MAX;
+		a->chars[i++] += 1;
+	}
+
+	if (a->used < i)
+		a->used = i;
+	SET_SIGNUM(a, !zzero(b) | !zzero(c));
+}
+
+
+void
+zadd(z_t a, z_t b, z_t c)
+{
+	if (zzero(b)) {
+		if (a != b)
+			zset(a, c);
+	} else if (zzero(c)) {
+		if (a != b)
+			zset(a, b);
+	} else if (b == c) {
+		zlsh(a, b, 1);
+	} else if ((zsignum(b) | zsignum(c)) < 0) {
+		if (zsignum(b) < 0) {
+			if (zsignum(c) < 0) {
+				zadd_unsigned(a, b, c);
+				SET_SIGNUM(a, -zsignum(a));
+			} else {
+				zsub_unsigned(a, c, b);
+			}
+		} else {
+			zsub_unsigned(a, b, c);
+		}
+	} else {
+		zadd_unsigned(a, b, c);
+	}
+}