X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=tomsfastmath%2Fsrc%2Fbit%2Ffp_mod_2d.c;fp=tomsfastmath%2Fsrc%2Fbit%2Ffp_mod_2d.c;h=d2818f034203d4d45b80fe633b7d0e4dce62bc31;hb=66bc25938679f1d6a1d1200f329093d82a5e99b4;hp=0000000000000000000000000000000000000000;hpb=a52ee0733f420ca20224049260d6fc5cf7d8f621;p=zpackage

diff --git a/tomsfastmath/src/bit/fp_mod_2d.c b/tomsfastmath/src/bit/fp_mod_2d.c
new file mode 100644
index 0000000..d2818f0
--- /dev/null
+++ b/tomsfastmath/src/bit/fp_mod_2d.c
@@ -0,0 +1,42 @@
+/* TomsFastMath, a fast ISO C bignum library.
+ * 
+ * This project is meant to fill in where LibTomMath
+ * falls short.  That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ * 
+ * Tom St Denis, tomstdenis@gmail.com
+ */
+#include <tfm_private.h>
+
+/* c = a mod 2**d */
+void fp_mod_2d(fp_int *a, int b, fp_int *c)
+{
+   int x;
+
+   /* zero if count less than or equal to zero */
+   if (b <= 0) {
+      fp_zero(c);
+      return;
+   }
+
+   /* get copy of input */
+   fp_copy(a, c);
+ 
+   /* if 2**d is larger than we just return */
+   if (b >= (DIGIT_BIT * a->used)) {
+      return;
+   }
+
+  /* zero digits above the last digit of the modulus */
+  for (x = (b / DIGIT_BIT) + ((b % DIGIT_BIT) == 0 ? 0 : 1); x < c->used; x++) {
+    c->dp[x] = 0;
+  }
+  /* clear the digit that is not completely outside/inside the modulus */
+  c->dp[b / DIGIT_BIT] &= ~((fp_digit)0) >> (DIGIT_BIT - b);
+  fp_clamp (c);
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */