commit files needed for zpm-fetchurl

[zpackage] / tomsfastmath / src / mul / fp_mul_2d.c

diff --git a/tomsfastmath/src/mul/fp_mul_2d.c b/tomsfastmath/src/mul/fp_mul_2d.c
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+/* 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 * 2**d */
+void fp_mul_2d(fp_int *a, int b, fp_int *c)
+{
+   fp_digit carry, carrytmp, shift;
+   int x;
+
+   /* copy it */
+   fp_copy(a, c);
+
+   /* handle whole digits */
+   if (b >= DIGIT_BIT) {
+      fp_lshd(c, b/DIGIT_BIT);
+   }
+   b %= DIGIT_BIT;
+
+   /* shift the digits */
+   if (b != 0) {
+      carry = 0;   
+      shift = DIGIT_BIT - b;
+      for (x = 0; x < c->used; x++) {
+          carrytmp = c->dp[x] >> shift;
+          c->dp[x] = (c->dp[x] << b) + carry;
+          carry = carrytmp;
+      }
+      /* store last carry if room */
+      if (carry && x < FP_SIZE) {
+         c->dp[c->used++] = carry;
+      }
+   }
+   fp_clamp(c);
+}
+
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */