1 files changed, 54 insertions, 0 deletions
diff --git a/libtommath/bn_mp_get_bit.c b/libtommath/bn_mp_get_bit.c
new file mode 100644
index 0000000..fc2d76e
--- /dev/null
+++ b/libtommath/bn_mp_get_bit.c
@@ -0,0 +1,54 @@
+#include "tommath_private.h"
+#ifdef BN_MP_GET_BIT_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.
+ *
+ * SPDX-License-Identifier: Unlicense
+ */
+
+/* Checks the bit at position b and returns MP_YES
+   if the bit is 1, MP_NO if it is 0 and MP_VAL
+   in case of error */
+int mp_get_bit(const mp_int *a, int b)
+{
+   int limb;
+   mp_digit bit, isset;
+
+   if (b < 0) {
+      return MP_VAL;
+   }
+
+   limb = b / DIGIT_BIT;
+
+   /*
+    * Zero is a special value with the member "used" set to zero.
+    * Needs to be tested before the check for the upper boundary
+    * otherwise (limb >= a->used) would be true for a = 0
+    */
+
+   if (mp_iszero(a) != MP_NO) {
+      return MP_NO;
+   }
+
+   if (limb >= a->used) {
+      return MP_VAL;
+   }
+
+   bit = (mp_digit)(1) << (b % DIGIT_BIT);
+
+   isset = a->dp[limb] & bit;
+   return (isset != 0u) ? MP_YES : MP_NO;
+}
+
+#endif
+
+/* ref:         HEAD -> master, tag: v1.1.0 */
+/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
+/* commit time: 2019-01-28 20:32:32 +0100 */