version 0.3.33

[fms.git] / libs / libtommath / bn_mp_sub.c

diff --git a/libs/libtommath/bn_mp_sub.c b/libs/libtommath/bn_mp_sub.c
new file mode 100644 (file)
index 0000000..a69d032
--- /dev/null
+++ b/libs/libtommath/bn_mp_sub.c
@@ -0,0 +1,59 @@
+#include <tommath.h>
+#ifdef BN_MP_SUB_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis
+ *
+ * LibTomMath is a library that provides multiple-precision
+ * integer arithmetic as well as number theoretic functionality.
+ *
+ * The library was designed directly after the MPI library by
+ * Michael Fromberger but has been written from scratch with
+ * additional optimizations in place.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
+ */
+
+/* high level subtraction (handles signs) */
+int
+mp_sub (mp_int * a, mp_int * b, mp_int * c)
+{
+  int     sa, sb, res;
+
+  sa = a->sign;
+  sb = b->sign;
+
+  if (sa != sb) {
+    /* subtract a negative from a positive, OR */
+    /* subtract a positive from a negative. */
+    /* In either case, ADD their magnitudes, */
+    /* and use the sign of the first number. */
+    c->sign = sa;
+    res = s_mp_add (a, b, c);
+  } else {
+    /* subtract a positive from a positive, OR */
+    /* subtract a negative from a negative. */
+    /* First, take the difference between their */
+    /* magnitudes, then... */
+    if (mp_cmp_mag (a, b) != MP_LT) {
+      /* Copy the sign from the first */
+      c->sign = sa;
+      /* The first has a larger or equal magnitude */
+      res = s_mp_sub (a, b, c);
+    } else {
+      /* The result has the *opposite* sign from */
+      /* the first number. */
+      c->sign = (sa == MP_ZPOS) ? MP_NEG : MP_ZPOS;
+      /* The second has a larger magnitude */
+      res = s_mp_sub (b, a, c);
+    }
+  }
+  return res;
+}
+
+#endif
+
+/* $Source: /cvs/libtom/libtommath/bn_mp_sub.c,v $ */
+/* $Revision: 1.3 $ */
+/* $Date: 2006/03/31 14:18:44 $ */