X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=tomsfastmath%2Fsrc%2Faddsub%2Ffp_sub.c;fp=tomsfastmath%2Fsrc%2Faddsub%2Ffp_sub.c;h=c482a6af87a1e69ee37f051c1b1cdb21c6110499;hb=66bc25938679f1d6a1d1200f329093d82a5e99b4;hp=0000000000000000000000000000000000000000;hpb=a52ee0733f420ca20224049260d6fc5cf7d8f621;p=zpackage

diff --git a/tomsfastmath/src/addsub/fp_sub.c b/tomsfastmath/src/addsub/fp_sub.c
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+++ b/tomsfastmath/src/addsub/fp_sub.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 - b */
+void fp_sub(fp_int *a, fp_int *b, fp_int *c)
+{
+  int     sa, sb;
+
+  sa = a->sign;
+  sb = b->sign;
+
+  if (sa != sb) {
+    /* subtract a negative from a positive, OR */
+    /* subtract a positive from a negative. */
+    /* In either case, ADD their magnitudes, */
+    /* and use the sign of the first number. */
+    c->sign = sa;
+    s_fp_add (a, b, c);
+  } else {
+    /* subtract a positive from a positive, OR */
+    /* subtract a negative from a negative. */
+    /* First, take the difference between their */
+    /* magnitudes, then... */
+    if (fp_cmp_mag (a, b) != FP_LT) {
+      /* Copy the sign from the first */
+      c->sign = sa;
+      /* The first has a larger or equal magnitude */
+      s_fp_sub (a, b, c);
+    } else {
+      /* The result has the *opposite* sign from */
+      /* the first number. */
+      c->sign = (sa == FP_ZPOS) ? FP_NEG : FP_ZPOS;
+      /* The second has a larger magnitude */
+      s_fp_sub (b, a, c);
+    }
+  }
+}
+
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */