1 files changed, 63 insertions, 0 deletions
diff --git a/libtommath/bn_mp_lshd.c b/libtommath/bn_mp_lshd.c
new file mode 100644
index 0000000..398b648
--- /dev/null
+++ b/libtommath/bn_mp_lshd.c
@@ -0,0 +1,63 @@
+#include <tommath.h>
+#ifdef BN_MP_LSHD_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@iahu.ca, http://math.libtomcrypt.org
+ */
+
+/* shift left a certain amount of digits */
+int mp_lshd (mp_int * a, int b)
+{
+  int     x, res;
+
+  /* if its less than zero return */
+  if (b <= 0) {
+    return MP_OKAY;
+  }
+
+  /* grow to fit the new digits */
+  if (a->alloc < a->used + b) {
+     if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
+       return res;
+     }
+  }
+
+  {
+    register mp_digit *top, *bottom;
+
+    /* increment the used by the shift amount then copy upwards */
+    a->used += b;
+
+    /* top */
+    top = a->dp + a->used - 1;
+
+    /* base */
+    bottom = a->dp + a->used - 1 - b;
+
+    /* much like mp_rshd this is implemented using a sliding window
+     * except the window goes the otherway around.  Copying from
+     * the bottom to the top.  see bn_mp_rshd.c for more info.
+     */
+    for (x = a->used - 1; x >= b; x--) {
+      *top-- = *bottom--;
+    }
+
+    /* zero the lower digits */
+    top = a->dp;
+    for (x = 0; x < b; x++) {
+      *top++ = 0;
+    }
+  }
+  return MP_OKAY;
+}
+#endif