X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=tomsfastmath%2Fsrc%2Faddsub%2Fs_fp_sub.c;fp=tomsfastmath%2Fsrc%2Faddsub%2Fs_fp_sub.c;h=dc03f0a55908bbca28a54ff428b62a12739a015f;hb=66bc25938679f1d6a1d1200f329093d82a5e99b4;hp=0000000000000000000000000000000000000000;hpb=a52ee0733f420ca20224049260d6fc5cf7d8f621;p=zpackage

diff --git a/tomsfastmath/src/addsub/s_fp_sub.c b/tomsfastmath/src/addsub/s_fp_sub.c
new file mode 100644
index 0000000..dc03f0a
--- /dev/null
+++ b/tomsfastmath/src/addsub/s_fp_sub.c
@@ -0,0 +1,40 @@
+/* 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>
+
+/* unsigned subtraction ||a|| >= ||b|| ALWAYS! */
+void s_fp_sub(fp_int *a, fp_int *b, fp_int *c)
+{
+  int      x, oldbused, oldused;
+  fp_word  t;
+
+  oldused  = c->used;
+  oldbused = b->used;
+  c->used  = a->used;
+  t       = 0;
+  for (x = 0; x < oldbused; x++) {
+     t         = ((fp_word)a->dp[x]) - (((fp_word)b->dp[x]) + t);
+     c->dp[x]  = (fp_digit)t;
+     t         = (t >> DIGIT_BIT)&1;
+  }
+  for (; x < a->used; x++) {
+     t         = ((fp_word)a->dp[x]) - t;
+     c->dp[x]  = (fp_digit)t;
+     t         = (t >> DIGIT_BIT)&1;
+   }
+  for (; x < oldused; x++) {
+     c->dp[x] = 0;
+  }
+  fp_clamp(c);
+}
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */