mescc: Mes C Library: Add integer division algorithm.

* lib/mes/div.c: New file.

lib/mes/div.c

@@ -0,0 +1,78 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * GNU Mes --- Maxwell Equations of Software
+ * Copyright © 2016,2017,2018,2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ * Copyright © 2019 Danny Milosavljevic <dannym@scratchpost.org>
+ *
+ * This file is part of GNU Mes.
+ *
+ * GNU Mes is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * GNU Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <mes/lib.h>
+#include <assert.h>
+#include <stdint.h>
+#include <limits.h>
+
+/*#define LONG_MIN (-(~0UL>>1)-1)*/
+
+typedef struct
+{
+  long quot;
+  long rem;
+} ldiv_t;
+
+void __mesabi_div0(void)
+{
+  eputs(" ***MES C LIB*** divide by zero numerator=");
+  eputs("\n");
+  assert(0);
+}
+
+/* Compare gcc: __udivdi3 */
+unsigned long __mesabi_uldiv(unsigned long a, unsigned long b, unsigned long* remainder)
+{
+  unsigned long tmp;
+  if (!remainder)
+    remainder = &tmp;
+  *remainder = 0;
+  if (b == 1)
+    return a;
+  else if (b == 0)
+    __mesabi_div0();
+  else
+    {
+      unsigned long x;
+      for (x = 0; a >= b; a -= b)
+        ++x;
+      *remainder = a;
+      return x;
+    }
+}
+
+/* Note: Rounds towards zero */
+ldiv_t ldiv(long a, long b)
+{
+  ldiv_t result;
+  int negative_result = (a < 0) ^ (b < 0);
+  assert(a != LONG_MIN && b != LONG_MIN);
+
+  if (a < 0)
+    a = -a;
+  if (b < 0)
+    b = -b;
+  result.quot = __mesabi_uldiv(a, b, &result.rem);
+  if (negative_result)
+    result.quot = -result.quot;
+  return result;
+}